Antivirus woes

[Arnobius]

Upgraded from Kaspersky Antivirus 5.0 to 6.0 and hit a snag. To protect from viruses, it seems the program writeprotected my files so I can no longer do a boot defrag with Diskeeper and my games no longer work. I can't undo this even by doing a System Restore. Anyone have any ideas or am I basically screwed and have to do a clean install?