that's happened to me on wallets before if the qt closed wrong or my comp crashed... I usually end up re downloading the the blockchain.

Save your wallet.dat file somewhere safe then delete your bitb apps/roaming file (or open the file and delete everything but your wallet.dat) then re open the wallet.

on windows you can find your roaming file in your local harddrive click on  users/(your user/comps name)/AppData/Roaming... there you will find your bitb file along with any other coins files you might have.