This usually indicates a badly-initialised pointer - either it's zero and shouldn't be, or it is fooling a test-for-zero check through being filled with random garbage, and thus preventing program flow from correctly returning to the calling function. Suggest running the debugger to see if the problem goes away - this indicates the second issue, as the debugger will initialise all pointers not given an explicit value to zero; if it persists, you should at least be able to get a stack trace.