Yeah...sometimes folks will have that kind of problem with the antivirus softwares.
One place that is free to do a virus check (and I recommend always using more than one) is here -
http://housecall.trendmicro.com/
The reason I suggest this is because not all antivirus software programs have every single up to date virus in their repetoire. I've found viruses and trojans through this free scan that weren't found by Symantic.
It's free, and you can scan while surfing the net. It can also be used when using an installed antivirus software such as McAffee or Symantic or any other out there.

sabby