Vista - Problem with printer port

HI i've developed a simple printer driver that doesn't communicate with a
physical printer but instead creates a PDF or TIF file for every page.

Now i've written an application to automate printer installation
The app does this:
- copy driver files
- install new driver
- creates a new local port
- creates a new printer

and vverything workf fine(the install is run as administrator).
The problem is that when i try to use the printer with a non-admin user it
doesn't and i get this message in the event viewer

Event Type: Error
Event Source: Print
Event Category: None
Event ID: 6161
Date: 21/5/2008
Time: 6:31:33 PM
User: NICOLAXP\Roberto
Computer: NICOLAXP
Description:
The document Test Page owned by Roberto failed to print on printer
EasyPrinter. Data type: NT EMF 1.008. Size of the spool file in bytes:
74996. Number of bytes printed: 0. Total number of pages in the document: 1.
Number of pages printed: 0. Client machine: \\NICOLAXP. Win32 error code
returned by the print processor: 5 (0x5).
For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.



The problem is the same if a manully install the driver and manully create
the local port.
Setting the printer non to spool will not resolve the problem, i've also
added full control to everyone to the c:\windows\system32 folder.

PLEASE HELP
Regards
Nicola