Airbird, have you just started getting this ? I used to get this alot with V7, it happens when the connection times out to Grisoft's servers at busy periods. Give it a few hours and try again. If you still havent got an update after about three days, then go to the Grisoft ste and manually download the latest definitions. Pain in the a*** I know, butat least it keeps you safe.
Bests
Giz