Activate-Callback doesn't works


I set an activation-callback for my elements dynamically:

int DActivate( PtWidget_t *widget,TprPhClass_t *Obj,PtCallbackInfo_t *cbinfo )

PtAddCallback(MyWidget, Pt_CB_ACTIVATE, ( PtCallbackF_t *)DActivate, Obj );

The PtAddCallback()-function is called. Nevertheless DActivate() is not executed when I left-click MyWidget.

What could be the reason for that?

Just as an additinal information: The code does not work on QNX 6.3.2 but on older versions of the operating system there is no problem.