>But after removing all debugger statements it does not work anymore and my second window is just gray.
>When I activate the set-step-on-command again, it works within the IDE.
>I tried to replace the set-step-on-statement with doevents andor the windows apu-function sleep but without any success.
>So my question ist, what else rhe set-step-on-command is doing and how can I get it working.
>
You already tried the first band aid with doEvents.
My next steps would be some versions of wait window (not only DoEvents called, but screen output thrown into), trying several options like timeout and so on.
After that probably activating some other process and resetting focus back to vfp (check how you set up YOUR debug window...)

HTH