The recent AVG 2011 update 3292, is cumbersome for Windows 7 64-bit OS customers because after getting this update you are unable to boot to your operating system. Certainly, AVG has got hold of this serious problem and issued a fix for the same.
Read the tips or watch the step-by-step video guide below to fix this issue:
Tips for users affected by AVG 271.1.1/3292 (432/3292) definition update:
Users who have downloaded the 3292 update, prompted for a restart, but did not restart their system, please download fixcorex utility and run it. After running this utility it is safe to restart your computer.
Users who have downloaded the update and applied the system restart should follow the instructions provided in this official tutorial.
Users who are running Windows 7 and have not downloaded and installed this update  are ok and no action is necessary.
Source: AVG official blog