Problems with os.rename

[loial]

I am having problems with os.rename on AIX

The source file definately exists and the target file does not.
However the rename always generates an  OSerror exception.   I can do
the rename via a mv statement at the AIX command line with no problem.

How can I get more info what the cause of the OSError exception is?

N.B. The source file is created by a process run via subprocess e.g.

       from subprocess import Popen, PIPE, STDOUT
       p = Popen(self.command, stdout=PIPE, stderr=STDOUT, shell=True)
       return p.wait()

Could this be the issue?