As soon as the trial add-ons are removed viewtopic.php?f=76&t=4668#p17085 (in my case it's Linux), and Qcad is restarted, the FlexPainter doesn't work. Only straight lines are painted (for instance "RulerMetrics" works whereas "SinusoidWave" doesn't work).Did you ran it with the debugger? Where does it fail?
Could it be that it involves unsupported entity types?
An idea, when switching from PRO to CE, would be to remove only those "Painter Set"s that use PRO add-ons.