Python/Numpy error: NULL result without error in PyObject_Call
That message comes directly from the CPython interpreter (see abstract.c method PyObject_Call). You may get a better response on a Python or NumPy mailing list regarding that error message because it looks like a problem in C code. 
Write a simple example to demonstrating the problem and you should be able to narrow the issue down to a module then a method.
I've never seen this error before, and none of the hits on Google seem to apply. I've got a very large NumPy array that holds Boolean values. When I try writing the array using numpy.dump(), I get the following error:
SystemError: NULL result without error in PyObject_Call
The array is initialized with all False values, and the only time I ever access it is to set some of the values to True, so I have no idea why any of the values would be null.
When I try running the same program with a smaller array, I get no error. However, since the error occurs at the writing step, I don't think that it's a memory issue. Has anybody else seen this error before?