Service runs in session != 0 but fails in session 0

Question

I have a service that executes a .bat file that calls a python program. The python program includes the win32com module.

If the service is run as session 0 it fails somewhere deep in win32com.

However, if the service is run as session != 0, it executes OK. Similarly, if the .bat file is executed from a cmd window at the desktop it runs OK.

Any thoughts about why this is happening?