It sounds like a corrupted file to me.
This might benefit form running the Virtual Technician to see if it can fix things. If that doesn't work then do as follows:
Enable Windows Firewall as a precaution
Uninstall all McAfee products via Control Panel/Programs/Uninstall a Program
Run the MCPR removal tool
Reinstall everything from your online account.
I trust your Vista is SP2? I ask because support for Vista (no service packs) has ended.