AVG free discussion forums have indicated this may be server overload at their end. If all else fails then a manual download from the Grisoft.com web site seems to work every time - you simply update from the folder into which you downloaded the update.
Sethhaniel, don't worry mate. Found it. I had my AVG setup to download from the Internet. Have changed it so it asks me every time whether I want from Internet or Folder. Now works and have done the update.