Using the debugger, once setup, was easier than thought. Unfortunately the come out wasn't worth the effort.
The error seems to change position sometimes. At the end I can tell, that location and/or size of an object (bitmap) shall be resolved. Last registered access is to ntdll.dll and allegro.../bitmap.c. There the value 0x0 is returned. I guess the value shouldn't be 0x0, thus crashing the program.
All object are in good order :-) and I do not understand this behaviour.
I found, when I use my function BM_h() - returning height of a bitmap, there will be a wrong value. Just now, program crashed with -5901xxxxx. I guess negative values are not possible.