Debugging a program under windows.

Hello,

I have a "ghost" bug in a rather big project occurring only when running the "Release" version of the program, and i would like to know what options i have to be able to debug such issue, when the program crashes the stack isn't very of any help since no debugging symbols are available for the "Release" version of the Qt libs...

The stack looks like that (But i'm not even sure it's the faulty thread =/ ):
0 0xffffffff86d2d768
1 0x17cda50
2 QThread::start QtCore4 0x670257bc
3 QThread::setTerminationEnabled QtCore4 0x67024ccb
4 QThread::setPriority QtCore4 0x670250c3
5 _threadstartex threadex.c 326 0x785434c7
6 BaseThreadStart kernel32 0x7c80b729

Stack level 0 shows ASM:
0x86d2d668 <+0x0000> ???
^ Memory access error in 'u 0xffffffff86d2d668 0xffffffff86d2d868'

Stack at level 2: the dissembler hooks up at the last line of those:
0x670257ab <+0x06cb> call QtCore4!QEventDispatcherWin32::trUtf8+0x50 (67024710)
0x670257b0 <+0x06d0> mov eax,dword ptr [QtCore4!QEventTransition::staticMetaObject+0x664b8 (672546fc)]
0x670257b5 <+0x06d5> push eax
0x670257b6 <+0x06d6> call dword ptr [QtCore4!QTextCodec::codecForIndex+0x19a74 (6715d054)]
0x670257bc <+0x06dc> mov esi,eax

Stack level 3: the dissembler hoops up at the last line of those:
0x67024cc6 <+0x0036> call QtCore4!QMutexLocker::QMutexLocker (6700bad0)
0x67024ccb <+0x003b> mov al,byte ptr [esp+24h]

How one would solve such problem?
Thanks!
Pierre.