Debugging Problems

I have been trying to run the VC++ debugger but am running into problems. I'm hoping somebody can lead me in the right direction here. As I start the debugging I get a message something like 'User Breakpoint called from code at 0x77f76274' and the following in the variables window:

Context: NTDLL! 77f76274 this CXX0017: Error: symbol "this" not found

with the following disassembly:

77F76274 int 3
77F76275 ret
77F76276 mov eax,eax
77F76278 int 3
77F76279 ret
77F7627A mov eax,eax
77F7627C mov eax,dword ptr [esp+4]
77F76280 int 3
77F76281 ret 4
77F76284 push ebp
77F76285 lea eax,dword ptr [esp+0Ch]

The program is partly running and is getting at least part way through OnInitDialog since I can see it initializing MSCOmm ActiveX controls I have. But it never gets to paint the window. (I am running a dialog based application).
When I just execute it it seems to run ok, ( with the occasional crash).

Any clues where to start tracking this down.

Thanks
cve

I get debug messages like that sometimes when my program failed an ASSERTion, most times an assertion I added myself.
Rudolf