Go back to the code and analyse and code-review it; if possible create some (unit)test functions to try to catch the offensive code.
Are you certain you are not leaking memory ? missing a few free/delete here and there ?
Are you certain you are checking all pointers (against NULL/nullPtr) before using them ?
There are tools to catch memory leaks, VLD is simple and free (
http://vld.codeplex.com/[
^] ) it should help you get a good start.
Good luck.