Afif,

unfortunately, the code and information you posted doesn't tell the whole story. One thing sticking out, though, is that
 you seem to use two arrays of widget pointers (my_label[] and my_label2[]) and two indices into these arrays (a and b) 
which keep being incremented on every timer tick. I don't know the exact sizes of the arrays, but letting the indices 
increase without bounds seems like a bad idea no matter how large the arrays are - sooner or later, you'll always be 
using "entries" beyond the array boundaries and will experience all kinds of effects. 

Also, since PtUnrealizeWidget() doesn't actually delete the widget object, you currently keep piling up unrealized 
widgets in the background. That's not what makes the application crash, but it causes a memory leak and will deteriorate
 the GUI's performance over time. 

Personally, I'd suggest using two arrays of six entries each. Create (and if possible, also realize) the widgets only 
once at startup time. Then, at each timer tick, re-calculate every widget's position and use PtSetResource() to set the 
Pt_ARG_POS resource of the widgets. That way, you can just move the existing widgets around instead of creating new ones
 every time.

Regards,
Thomas