Did you make the template available to clients (The 'Make available to clients" button in the toolbar of Manage Software List under Reporting/Monitoring in your toolbox)?
be sure you pressed the button Make available to clients that you find under Tools -> Reporting -> Manage software List GUI?
If the problem persists you can try to modify the link that points to the Inventory Scanner on one of your 'test' client appending these parameters/F /SYNC /O=%temp%\myscan.scn and launch it.
When if finishes it will generate the file %temp%\myscan.scn. Open it with notepad and look for .PST so you will be able to verify if the scanner is working fine.
If you want to do more complex evalutation about your PST files or other aspects of the Inventory Scanner you can have a look to this article:
StockTrader - Marco