I think we're discussing two different things.
The debugger screen you are talking about is enabled with _mod_on_off.h and the line:
#define MOD_BETTATESTMODE "On" // On -DEV version; Test - TST ver; Off
If "On", then F11 will launch the screen you are talking about and debugwindow=1 in start.ini has no effect.
I thought you wanted this screen:
This is enabled with start.ini setting dbgwindow = 1, then hit F5. I thought that is what you were trying for.
Yes, if you have a script error in Program\debuger.c, it will not launch.