I think it was some kind of mistake in key generation, if I was you I just registered it once again, to see if I’ll get the same result with the new key recieved.
I just noticed that the registration key in About avast! was not the one I obtained and entered in January this year. I re-entered that key, and now my updates are good to 2007, not April 1 this year.
What could have caused the key to change?
I’m using avast! Home here, so I haven’t been entering any dodgy crack keys or anything! 8)