On a Windows system which supports runas
. First, independently run your program by launching it from a command line which was run as that user, like following
runas /user:<domain\username> cmd
Then, in that new command line, cd
to the path from where you expect the task launcher to launch your program and type the full arguments, for example.
cd D:\Scripts\
, then execute
C:\python27\pthon.exe script.py
Any errors that are being suppressed by task scheduler should come out to command line output and will make things easier to debug.