Operation failed due to network or other comm. problems

Error message: "The operation failed due to network or other communication problems.  Please check your connection and try again"

Never EVER seen this problem.  It happens when I click Send in Outlook.  The program is use to compose mail is MS Word.  This is Outlook 2002 SP1 and Office XP.

I have been researching this on the web.  I found a microsoft article that told me to delete a certain registry key and then run an Outlook repair.  I did that and thought it fixed it, but the problem is back.  It happens about once every 5-10 times I send a mail.  

I have also tried re-installing Outlook altogether with no luck.

I found one article (dont know how legitimate it was) that suggested Norton AV may be the problem.  This makes absolutely no sense because I installed NAV over 7 months ago and this problem has just come up.  I haven't recently installed any huge programs and I haven't uninstalled any either.

What in the world is causing this?  Anybody ever seen it before?  Any suggestions or tips would be greatly appreciated.  Also this is one machine on a 30 computer network-- all configured the same and this is the only one with this prob.  It's a winXP machine if you need that info too.

Thanks a lot!
-dan