Outlook 2k printer problem

OS NT 4.0 Sp 6a, all Printers disappear after printing an email. Have Norton Corp. anti-virus 7.5 with up to date definitions. This happens only sporatically, and once an email does this, it will always do this. Have run virus scans on machine andexchange server and the scan finds nothing. Have to re-boot to to get printers back.
What the heck is going on?