Connection time out error Outlook XP - related DCOM Error 10005 in Event Viewer

I have a small 25 user network where several of the PC's have started having intermittent connection problems in Outlook XP.   Generally the Outlook connection to an external POP Server will time out.   Often the user will have to exit Outlook as it hangs.   On retarting Outlook they will often end up with multiple instances of Outlook.exe running.   At this point it becomes necessary to reboot the PC.   At no time do the effected systems lose their network or internet connectivity.

Systems concerned are all Dell PC's running XP Pro & Office XP with all current patches applied.   Anti virus software is VET Enterprise Edition.   The network config is a workgroup with no DC.   Email is a collection of POP3 accounts on an external server.   All the PC's are identical both in hardware and software yet the problem is only occuring on some of the PC's.   All systems are free of Spyware and virus definitions are upto date.   There appears to be no rogue services running and the msconfig file has nothing unusual in it.

Event Viewer for the effected PC's shows a DCOM error Event ID 10005, DCOM got error "The service cannot be started, either because it is disabled or because it has no enabled devices associated with it." "attempting to start the service MDM with arguments"" in order to run the server:

I have tried reinstalling Outlook along with Service Pack3 and have run all the various patches available via Windows Update for XP.   I have also used scanpst on the offending PC's PST files.   I have exported couple of the users email to Outlook Express 6 and have had no connection problems using Outlook Express.

The problem appears to be Outlook specific and the DCOM error on the MDM Service appears on all of them.

Any ideas?   My last resort is to reformat and reinstall but I would prefer to get to the bottom of this and find the cause.