Thanks for the idea! I'll try it.
Another way I was trying was using the ON KEY LABEL with the sys(1500) to activate the _MED_COPY and _MED_PASTE parts of the _MEDIT menu. Here is the code I used in the main program:

ON KEY LABEL CTRL+C SYS(1500, '_MED_COPY', '_MEDIT')
ON KEY LABEL CTRL+V SYS(1500, '_MED_PASTE', '_MEDIT')
ON KEY LABEL CTRL+A SYS(1500, '_MED_SLCTA', '_MEDIT')

The CTRL+V works fine and pastes anything in that is on the clipborad.
The CTRL+A works also and highlights everything in the textbox.
But the CTRL+C will not put the highlighted text in the clipboard.
I even tried the following, but nothing works.

ON KEY LABEL CTRL+C _CLIPTEXT = SYS(1500, '_MED_COPY', '_MEDIT')

Any idea how to get the SYS(1500) copy or cut working?