C Wrapper Function, crashing Python?

[Java and Swing]

static PyObject *wrap_doStuff(PyObject *self, PyObject *args) {
	// this will store the result in a Python object
	PyObject *finalResult;

	// get arguments from Python
	char *result = 0;
	char *in= 0;
    	char *aString = 0;
	char *bString = 0;
	MY_NUM *a;
	MY_NUM *b;
	int ok = PyArg_ParseTuple(args, "sss", &in, &aString, &bString);
	if (!ok) return 0;

	// do work to get a and b
	// count - returns an int;  GetVal - returns a char *
	a = GetVal(aString, count(aString, ","));
	b = GetVal(bString, count(bString, ","));

	// make function call, which returns a char *
	result = doStuff(in, a, b);

	// save result in Python string
	finalResult = PyString_FromString(result);

	// free memory
	PyMem_Free(result);
	PyMem_Free(a);
	PyMem_Free(b);

	// return the result as a Python string
	return finalResult;
}

...from python I can call this function 4 times...works fine.  WHen I
call it for the fifth time python.exe crashes.  im thinking some memory
problem in the wrapper function perhaps...but I am not sure.  The
actually C function, doStuff can be called 5, 6,7...N times without a
problem
so i know its gotta be my wrapper.

Any ideas?  Thanks!