Ah my dad used to have similar issues, I cleared all the data from alt.binz, in applications data (on XP) and the entire installation folder and reinstalled Alt.Binz. Solved it.
Except for 1 issue, if 1 or more blocks are missing, Alt.Binz wont auto download the amount of par2 needed and start the repair, it will just sit there doing nothing...
But if you unpause the par2 manually and let it download, it will go over to repair and unrar :S.
So try Clean reinstalling Alt.Binz and see if it works for you too!