ClamAV 0.94.x end of life.
As announced by the ClamAV Team in October, ClamAV 0.94.x has been disabled on April 15th by a signature in the virus database. For details see here:
http://www.clamav.net/lang/en/2009/10/05/eol-clamav-094/
If you have not updated ClamAV yourselves to at least 0.95.x, you will need to either disable virus checking or update ClamAV manually. Instructions can be found here:
http://osx.topicdesk.com/content/view/62/62/
HTH,
Alex
Mac OS X (10.6.3)