supnec smith

parameter vs freq

i can not plot the smith chart.when i plot the simulation would report error.
the following is the error message. what's mean?
??? Error using ==> impplot/impplot
Invalid Response Object passed to IMPPLOT

Error in ==> c:\snec\matlab\output\snecout.m (plotroutine)
On line 811 ==> impplot(DataToPlot);

Error in ==> c:\snec\matlab\output\snecout.m
On line 179 ==> plotroutine(gcf,PlotData);

??? Error while evaluating uicontrol Callback.