Ahah. This isn't a problem. It is the way BGT works. Basically you can't do them until you kill Sarevok, as it is now integrated into the game and you get a nice scene with Belt. If you really wanted to go you could CLUA yourself there, but I wouldn't advise as you may mess up some settings. Although I did it before and nothing went wrong, but then I didn't do all the quests.
My advice, keep going, you won't have any problems missing it out, and it is something to look forward to after killing the big S!
Good luck
