pw.x crashes with no error message at all.

This happens quite often in parallel execution, or under a batch queue, or if you are writing the output to a file. When the program crashes, part of the output, including the error message, may be lost, or hidden into error files where nobody looks into. It is the fault of the operating system, not of the code. Try to run interactively and to write to the screen. If this doesn't help, move to next point.