I got this the other day from an AVG update. Reboot and keep hitting F8 and select repair. Safe mode and start up repair will not work!
Go to a command prompt and rename the following -
program files (x86)/avg/avg10/avgrsa.exe
program files (x86)/avg/avg10/avgchsva.exe
you should be able to reboot, you will need to reinstall or repair AVG.
http://forums.avg.com/ww-en/avg-free-forum?sec=thread&act=show&id=132999 here is the support link from AVG