Script Host Client launched from Windows Service

Hello,

I have a client/server application that launches a Script Host application
from a Windows Service. The Script Host application launches Excel and opens
an xls file for processing.

This works on Windows 2000 and Windows XP, but on Vista we get an error from
Excel saying "cannot access the file: C:\foo.xls, there are a number of
possible reasons". The Script Host application works fine on Vista by
itself, but when launched from a Windows Service it does not have permission
to read the xls file.

Does anyone have any ideas as to what the problem may be? What extra things
do I need to do on Vista to get my Windows 2000/XP application to work?

Many thanks,
DavidRF