I think you need to establish if it's an error starting the script, or if it's an issue mapping the drive.
Try re-writing the script to have the first line just dump the current date/time to a text file. You can then check to see if the script runs at all, or if it does and is not mapping the drive for some reason.
An example batch script is:
md c:\logs
echo ---------------- >> c:\logs\loginscript.txt
date /t >> c:\logs\loginscript.txt
time /t >> c:\logs\loginscript.txt
net use j: \\someserver\someshare
this outputs a file 'c:\logs\loginscript.txt' looking like:
----------------
Mon 13/09/2010
01:59 PM
