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    I'm not able to reproduce the error, I was able to rerun it without
    restarting the kernel. Maybe it would be a good idea to delete those
    lines which are not needed like import of modules you are not using.
    Start with a short clean script and use more code cells. If you want
    to display the plot inline you can produce a PNG file, see attached
    notebook. <br>
    <br>
    -Karin<br>
    <br>
    <div class="moz-cite-prefix">Am 09.07.19 um 19:18 schrieb Mark
      England:<br>
    </div>
    <blockquote type="cite"
      cite="mid:88CF2D71-D453-4340-8544-54745CEB2A05@gmail.com">
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      Hi Karin,
      <div class=""><br class="">
      </div>
      <div class="">Attached. It is very simple and doesn’t need any
        data (just map plotting). </div>
      <div class="">If you run it once, it should work, however if you
        rerun the plotting cell (perhaps try to change the latitude or
        something) it will give you that error.</div>
      <div class=""><br class="">
      </div>
      <div class="">Mark<br class="">
      </div>
      <br>
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      <div class="">
        <div><br class="">
          <blockquote type="cite" class="">
            <div class="">On 9 Jul 2019, at 10:02, Karin Meier-Fleischer
              <<a href="mailto:meier-fleischer@dkrz.de" class=""
                moz-do-not-send="true">meier-fleischer@dkrz.de</a>>
              wrote:</div>
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              <div style="word-wrap: break-word; -webkit-nbsp-mode:
                space; line-break: after-white-space;" class="">Hi Mark,
                <div class=""><br class="">
                </div>
                <div class="">sometimes I have similar problems using
                  notebook and PyNGL running with the same preconditions
                  and have to restart the kernel. I don’t know if it is
                  caused by PyNGL because I get other error messages. Is
                  it possible to send the .ipynb file with test data to
                  try to reproduce your errors?</div>
                <div class=""><br class="">
                </div>
                <div class="">-Karin<br class="">
                  <div class=""><br class="">
                    <blockquote type="cite" class="">
                      <div class="">Am 09.07.2019 um 18:52 schrieb Mark
                        England via pyngl-talk <<a
                          href="mailto:pyngl-talk@ucar.edu" class=""
                          moz-do-not-send="true">pyngl-talk@ucar.edu</a>>:</div>
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                          after-white-space;" class="">
                          <div class="">Hi there,</div>
                          <div class=""><br class="">
                          </div>
                          <div class="">I am trying to transition to
                            using PyNGL (using Jupiter Notebook, Python
                            v3.7.3) on my Mac (Mojave 10.14.5).</div>
                          <div class="">I am just trying to create
                            simple plots (code below, mostly taken from
                            the examples online. When I run the script
                            first, it works fine and the pdf is created
                            exactly as advertised. All the relevant
                            modules are loaded.</div>
                          <div class="">However if I re-run the plotting
                            section of code in the Notebook, I get this
                            error:</div>
                          <div class=""><br class="">
                          </div>
                          <div class="">
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:["Error.c":406]:ErrorInitialize:Only
                                one instance of ErrorClass is supported</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                initialize layer-Can't Create</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Error
                                Creating ErrorClass object</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                initialize layer-Can't Create</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                initialize layer-Can't Create</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:_NhlCreate:Unable
                                to access "default" App object</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:_NhlCreate:Invalid
                                Parent id #-4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:NhlGetValues:PID
                                #-4 is invalid</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:PID #-4
                                can't be found in NhlSetValues</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">warning:maximize_plots:
                                Invalid workstation. No plot
                                maximization can take place.</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:NhlDraw:
                                Invalid Layer Id: -4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                update Workstation with PID#-4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                clear Workstation with PID#-4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:NhlDraw:
                                Invalid Layer Id: -4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                update Workstation with PID#-4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                clear Workstation with PID#-4</span></div>
                            <div class="" style="margin: 0px;
                              font-stretch: normal; font-size: 11px;
                              line-height: normal; font-family: Menlo;"><span
                                class="" style="font-variant-ligatures:
                                no-common-ligatures;">fatal:Unable to
                                Destroy (Bad PID#0)</span></div>
                          </div>
                          <div class="" style="margin: 0px;
                            font-stretch: normal; font-size: 11px;
                            line-height: normal; font-family: Menlo;"><span
                              class="" style="font-variant-ligatures:
                              no-common-ligatures;"><br class="">
                            </span></div>
                          <span class="">I can only get the figure
                            again, if, in the Kernel menu, I ‘restart
                            and run all’. It seems to be a problem with
                            the graphics? I have xQuartz installed. From
                            a similar topic I found online,
                            they removed Ngl.end() at the end, however
                            that doesn’t work for me.</span>
                          <div class=""><span class=""><br class="">
                            </span></div>
                          <div class=""><span class="">Thanks,</span></div>
                          <div class=""><span class=""><br class="">
                            </span></div>
                          <div class=""><span class="">Mark</span></div>
                        </div>
                        _______________________________________________<br
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                    </blockquote>
                  </div>
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                      start; text-indent: 0px; text-transform: none;
                      white-space: normal; word-spacing: 0px;
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                      break-word; -webkit-nbsp-mode: space; line-break:
                      after-white-space;" class="">
                      <div style="letter-spacing: normal; text-align:
                        start; text-indent: 0px; text-transform: none;
                        white-space: normal; word-spacing: 0px;
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                        break-word; -webkit-nbsp-mode: space;
                        line-break: after-white-space;" class=""><br
                          class="">
                      </div>
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </blockquote>
        </div>
        <br class="">
        <div class="">
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            rgb(0, 0, 0); letter-spacing: normal; text-align: start;
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            class="">
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              normal; text-align: start; text-indent: 0px;
              text-transform: none; white-space: normal; word-spacing:
              0px; -webkit-text-stroke-width: 0px; word-wrap:
              break-word; -webkit-nbsp-mode: space; line-break:
              after-white-space;" class="">
              <div dir="auto" style="word-wrap: break-word;
                -webkit-nbsp-mode: space; line-break:
                after-white-space;" class="">
                <div style="color: rgb(0, 0, 0); font-family: Helvetica;
                  font-size: 12px; font-style: normal;
                  font-variant-caps: normal; font-weight: normal;
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                  <div class="" style="font-variant-ligatures: normal;
                    font-variant-east-asian: normal;
                    font-variant-position: normal; line-height: normal;"><font
                      class="" face="Garamond" color="#747474">Mark
                      England, PhD.</font></div>
                  <div class="" style="font-variant-ligatures: normal;
                    font-variant-east-asian: normal;
                    font-variant-position: normal; line-height: normal;"><font
                      class="" face="Garamond" color="#747474">Columbia
                      University,</font></div>
                  <div class="" style="font-variant-ligatures: normal;
                    font-variant-east-asian: normal;
                    font-variant-position: normal; line-height: normal;"><font
                      class="" face="Garamond" color="#747474"><i
                        class="">Bakhmeteff Research Fellow in Fluid
                        Mechanics, </i></font></div>
                  <div class="" style="font-variant-ligatures: normal;
                    font-variant-east-asian: normal;
                    font-variant-position: normal; line-height: normal;"><font
                      class="" face="Garamond" color="#747474">Email: <a
                        href="mailto:mre2126@columba.edu" class=""
                        moz-do-not-send="true">mre2126@columbia.edu</a>, <a
                        href="mailto:markengland20@gmail.com" class=""
                        moz-do-not-send="true">markengland20@gmail.com</a></font></div>
                  <div class="" style="font-variant-ligatures: normal;
                    font-variant-east-asian: normal;
                    font-variant-position: normal; line-height: normal;"><font
                      class="" face="Garamond" color="#747474">Website: <a
                        href="http://markrossengland.com" class=""
                        moz-do-not-send="true">markrossengland.com</a></font></div>
                </div>
              </div>
            </div>
          </div>
        </div>
        <br class="">
      </div>
    </blockquote>
    <br>
    <pre class="moz-signature" cols="72">-- 
Dipl. Geophys. Karin Meier-Fleischer
Visualization, NCL, CDO, PyNGL
Application Support

Deutsches Klimarechenzentrum GmbH (DKRZ)
Bundesstrasse 45a - D20146 Hamburg - Germany

Phone:    +49 (0)40 460094 126
Fax:      +49 (0)40 460094 270
E-Mail:   <a class="moz-txt-link-abbreviated" href="mailto:meier-fleischer@dkrz.de">meier-fleischer@dkrz.de</a>
URL:      <a class="moz-txt-link-abbreviated" href="http://www.dkrz.de">www.dkrz.de</a>

Geschäftsführer: Prof. Dr. Thomas Ludwig
Sitz der Gesellschaft: Hamburg
Amtsgericht Hamburg HRB 39784
</pre>
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