I am having a sort of strange problem with the intonation of my Warwick (5-string). The strings are in tune, but I noticed that the notes played at the higher frets are WAY off -- nearly 1/4 step on the G and B strings. So I tried to tune the bridge. I could get the E, A, and D tuned up fine but never could quite get the G or B right. The G at the 12th fret is about 1/6 step sharp, and the G at the 24th fret is nearly half a step sharp! What's causing this? I've read around on the boards here and seen everything from "use a different gauge string" to "cut the spring on your saddles in half". Help!