title: Object is Invalid or Deleted when pressing button and plotting
body: <p>Please help. The error says that the object is deleted.</p>
  <blockquote>
  <p>Error using handle.handle/get
  Invalid or deleted object.</p>
  <p>Error in C:\Program Files\MATLAB\R2011b\toolbox\matlab\graph2d\plotyy.p&gt;localUpdatePosition (line 373)</p>
  <p>Error in C:\Program Files\MATLAB\R2011b\toolbox\matlab\graph2d\plotyy.p&gt;@(obj,evd (localUpdatePosition(obj,evd,ax(1),ax(2))) (line 212)</p>
  </blockquote>
  <p>I really do not understand what was deleted but every time I perform the impz(signal), the plot isn't showing the correct graph unlike the plot in freqz(signal) and zplane(signal).</p>
  <p>This is what really happens (26seconds video) - <a href="https://www.youtube.com/watch?v=HTR45lNIjuc" rel="nofollow noreferrer">https://www.youtube.com/watch?v=HTR45lNIjuc</a></p>
  <p>Line 212 contains this code <code>handles.N = str2num(get(handles.edtOrder,'String'));</code>
  Line 373 contains this code <code>zplane(handles.axPlots,handles.firVector,1)</code></p>
  <p>Code for impulse response</p>
  <pre><code>if (get(handles.cbImpResp,'Value') == 1)
          set(handles.txtPlotAvail,'Visible','off');
          switch (handles.filterValue)
              case 'FIR'
                  impz(handles.axPlots,handles.firVector,1)
              case 'IIR'
                  impz(handles.axPlots,handles.vectorB,handles.vectorA)
              case 'Multiple Bandpass'
          end
      else
          set(handles.txtPlotAvail,'Visible','on');
  end
  </code></pre>