Software Deployment

Hi all,
Hope to get some feedback and possible solution to a growing problem in our environment.

History:
Running NW6.0 and Zenworks for desktop version 4 on the XP Pro Workstations.

Rebuilding ALL applications that is not already MSI installation for distribution through Application explorer (NW zen)
The user GPO prevents users from installing applications or drivers by their own, and is hiding the C: (still availabel but not seen and no rights more than nessesary)
96% of all the applications are distributet perfectly, but some (often ready msi installations) tend to return a 53331 error.
This error seems to be that the installation runs out of diskspace in the C:\ drive.
This is not so, There are 3GB disk available on the C: and the installation runs perfect when logged in with admin rights on the local machine.

I am totally stuck in where to find the solution,
Please help