DCOM Error

Starting the morning or 1/12/05 all of my Windows XP SP1 PCs started getting a DCOM error in the system event log. This error repeats every 2-3 minutes. If I turn the windows firewall on, the error goes away. I can’t figure out what may be causing it. If anyone has any ideas, I would appreciate it. The error is as follows:

Event Type: Error
Event Source: DCOM
Event Category: None
Event ID: 10003
Date: 1/12/2005
Time: 9:02:16 AM
User: N/A
Computer: TN_RMOORE
Description:
Access denied attempting to launch a DCOM Server using DefaultLaunchPermssion. The server is:
{00020906-0000-0000-C000-000000000046}
The user is Unavailable/Unavailable, SID=Unavailable.
Data:

Thanks in advance