I have been using AVG antivirus free version for a few weeks on Windows XP. For the past 10 days my automatic virus definitions updates have been failing, showing various error messages:
"General error" in the popup alert in the bottom right corner of the screen (after an attempted update),
An "UPDATE FAILED" button to the right of the "Update now" button.
Clicking on the UPDATE FAILED button shows a page with:
AVG Guru