Hi, i was able to narrow the problem: 0009:CALL MFC42.823() ret=00ae484e 0009:Call msvcrt.malloc(00000031) ret=5f40384f 0009:Call ntdll.RtlAllocateHeap(00110000,00000000,00000031) ret=7ea60413 0009:trace:heap:RtlAllocateHeap (0x110000,70000062,00000031): returning 0xc11c70 0009:Ret ntdll.RtlAllocateHeap() retval=00c11c70 ret=7ea60413 0009:Ret msvcrt.malloc() retval=00c11c70 ret=5f40384f 0009:RET MFC42.823() retval=00c11c70 ret=00ae484e 0009:CALL MFC42.825() ret=003b16b5 0009:Call msvcrt.free(00c11c50) ret=5f40388b 0009:Call ntdll.RtlFreeHeap(00110000,00000000,00c11c50) ret=7ea603d4 0009:err:heap:HEAP_ValidateInUseArena Heap 0x110000: block 0xc11c70 tail overwritten at 0xc11ca1 (byte 0/15 == 0x00) Is that somehow useful? W.