This is really strange and I hope somebody can bring some sence to this

I have made a vbs script with a logging sub-routine:
- reads MachineGUID from Registry
- uses this to find some information in the hd_asset_view
- writes this data into another part of the registry
Every now and then I call the log-subroutine to see which values are used, etc
When I execute this on a client computer with cscript or wscript it runs suberb.

Now I need this to run real-time when I choose to. So a NS task seemed to be the best choice
First I entered this vbs script into the task, which failed.
I changed it to a command task that:
- copies the vbs script to %tmp%
- executes : start /wait wscript.exe temp3.vbs
- copies log file back to the NS-server
- pause
Then I saw what went wrong, but I do not understand.
WSH msg pops up with error: Login failed for user 'TEST\XPSP3$' (TEST is domain and XPSP3 is hostname client) code 80040E4D.

So Task is running on "Altiris Agent Credentials".
I changed that to specific user and used the same credential... IT WORKED!!!

So:
- locally it runs no matter what user
- as task with "Agent Credentials" is fails
- as task with specific user (the SAME as Agent Credentials!!!) is works!

Please enlight me... I am flabbergasted here. Bug by design?