Norton Antivrus and microsoft messenger

I have installed Norton Antivirus 2003 on my Win98 PC and it works fine. Howerv, as soon as i install MSN Messenger on my windows 98 pc i get the following error message periodically. Wether i am logged into MSN or not.
Norton Antivirus was unable to start the instant messenger scanner. It will be unable to scan instant messenger downloads for infections.
//I am using MSN version 5.0 & Norton AV 2003
I can click ok and the warning dialog box dissapears but it is really starting to annoy me. I have formatted the PC before because of this issue and thought that would cure the problem, obviously not. The thing is up until this week i had both running on the PC for months with no problems can anyone throw any suggestinos my way.

Thanks in advance