Check the attitude of your other party members towards you. I'm guessing they operate on the same scale as all NPCs - 0 is neutral, anything above that positive, below negative. +100 makes them allies, turning someone from yellow to green, while -X (??) makes them hostile, turning them from yellow to red. Unfortunately the scale is different for party members - you just get "neutral", "medium", "exceptional", etc - but it might give you an idea - if their opinion of you is already low, it won't take much for them to turn on you.
IF THIS IS THE CASE, pet Scratch. With your PC. A lot. Gale, Wyll and Shadowheart (and Astarion? I forget) all approve every time you do it until they max out. Once you get their approval high enough, no screw-up on your part should turn them against you. In theory, anyway.
