Problem with Printer Spooler Service

I know that this forum is for XP related issues, but I am desperate in my search for an answer on the following scenario.

I have a print server running Windows 2003 with the latest service packs and updates. For as long as I have been working at the company, there has been issues with printing every now and again. We have recently the problems have become much more frequent and we started to investigate the problems more seriously and found the following:

Each time the users are experiencing printing problems, there is a string of Event ID 6161 errors in the System Event Log. We found that an error occurs somewhere in the printing subsystem, but that the event is logged with an "error code 0 - Command completed successfully"

Restarting the printer spooler appears to solve the problem temporarily but we need to find a permanent solution to the problem.

Recently we also noticed that sometimes when we restart the printer spooler we are unable to see any local printers in the Printers and Faxes folder. When this occurs we are also unable to add any new local printers. These symptoms appears to be similar to a user who does not have admin rights on the machine, yet we are logging in with only one account and that account has full admin rights on the machine. Sometimes if you restart the printer spooler several times, the problem disappears and we can see all of the printers and add new local printers again. This is a strange problem which I have never seen before.

Any ideas?

Regards
EM