time to dig out your DOS skills
You need to boot the PC with a Windows CD and drop into the recovery console, or else use a "live" CD such as VistaPE and then delete that file manually
You then need to do a clean up of the PC......and quite simply AVG is not up to that
I've posted numerous times the steps needed to clean a machine....PM me if you need a refresher, I'm not posting them again
But believe me, just removing that file won't be enough -- there WILL be other crapware on that machine