An MAF message indicates that malloc has failed—you have run out of swap space for the heap to grow. After the message is delivered, malloc returns NULL in the normal manner.
Ideally, programs should handle out-of-swap conditions gracefully, but often do not. If your program next generates an NPR, NPW, ZPR or ZPW, and then a COR, a caller of malloc has failed to check the return status and is dereferencing the NULL pointer.