Try replacing Bases.cav. You will find it in the C:\Program Files\COMODO\COMODO Internet Security\scanners directory.
- Boot to safemode
- Go to C:\Program Files\COMODO\COMODO Internet Security\scanners
- Delete or rename bases.cav
- Go to C:\Program Files\COMODO\COMODO Internet Security\repair
- Copy bases.cav from C:\Program Files\COMODO\COMODO Internet Security\repair to C:\Program Files\COMODO\COMODO Internet Security\scanners
- Reboot
- Open CIS and update virus defs