Please try to follow these steps:
1. Please check the date/time settings on your computer (right-click on the clock on the task bar (in the right bottom corner of the screen) and choose the "Adjust Date/Time" option.
2. If the date/time settings are OK, you have possibly used more than a year old AVG Free Edition installation file. You can check your AVG Free Edition program version here: AVG Free Edition->Information->About AVG.
To solve this problem, please do the following:
* download the latest AVG Free Edition installation file, run this downloaded installation file
* choose the "Repair installation" option from the three possibilities offered
* finish that process
* if a computer restart is needed, please restart the computer
* update AVG Free Edition virus bases
It should then be OK. Generally, for a new AVG Free Edition installation we recommend you to use the latest version of the AVG Free Edition installation file. You can download it here.
Found it here: http://free.grisoft.com/doc/faq/us/frt/0/num/618#faq_618