Does your freshclam or clamd.log say anything that's suspect?
C:\Program Files (x86)\SmarterTools\SmarterMail\Service\Clam\log
You can verify your log settings are correct using the .conf files found here: C:\Program Files (x86)\SmarterTools\SmarterMail\Service\Clam\etc
Matt Petty
Software Developer
SmarterTools Inc.
(877) 357-6278
www.smartertools.com