...and because you're getting an error in it, you may have become infected with a virus or spyware. Then again, maybe you simply need to uninstall, then reinstall McAfee...At this point...Please tell us which version of McAfee Virus Scan you are using by RIGHT clicking on the McAfee shield, or red "M" in the lower right corner, choose 'About Virus Scan", then tell us the EXACT version you're using, the scan engine version and the virus definitions.

Next, please click on either, or both of the links below and run the free online scans they provide. Delete all infected files found:

Housecall Online Scanner

Panda Online Scanner

Next, download, install, update, then run ALL of the free spyware removal tools from the links below: