Time for a little trouble shooting... First things first, forget the barre chords for the moment, and just fret the single note on the B string that is giving you trouble in the chord form. Can you make it play cleanly? Can you play notes on the B string starting at the 1st fret, and move up above the 12th fret, one at a time, and have them all play cleanly, or is there a point where no matter how carefully you fret the single note on the B string, it just buzzes?

Also, what kind of guitar are you playing?