I've noticed on several computers that I've had to reinstall my AVG antivirus software (free edition). I finally connected it to running CCleaner Issues scan. It seems to be related to a file, avgamui.dll, which doesn't seem to exist, yet there are 3 entries in the registry for it which CCleaner removes. On the next reboot, AVG has to be repair reinstalled (and updated).
Another little glitch which doesn't seem to affect anything - It identifies .xpi as an Unused File Extension. ".xpi" are Firefox extension files, so it is not unused. I haven't noticed any negative effects when removing it, however.