Having issues playing barre chords (B Minor).. help?

I know there are two ways to play B-Minor, but my instructor wants me to learn to barre version (perhaps rightfully so, since I need to learn barres anyways). I am having issues playing the first string clearly. It plays once in awhile and when it does, it's very rattly. It seems that my middle finger (which is on the second string) mutes it the other times because my first string requries too much pressure, but then if I don't have the pressure on it, it's rattly... lol. There's no middle ground! Any suggestions for learning this barre?