User blog comment:Jackalex13/Is it a glitch or somethin?/@comment-3076194-20120204054509/@comment-4129359-20120204214809

Sorry, I got nothing. If you want my guess though, I'd suggest trying to get a different quest from one of the other companions, then try talking to Vilkas again after you do it. Another thing you can try is killing Lydia then asking Vilkas again, it may still be counting Lydia as a follower.