Buffalob, I had the exact problem as you. I tried many things, from widening my grip to narrowing it, to shoulder dislocations, and even bicep and other arm work. None of them helped.
I beat it, though, and solved the problem in one day. My issue was the bar position. I had the bar too low, and needed to lift my arms to support it. When supporting it incorrectly, all the weight was on my shoulders and hands.
To support the bar correctly, I had ignore the elbows up cue, and concentrate on really squeezing my shoulders back and together. This created a better shelf that is a bit further up on the back. With the bar held in this position, the majority of the weight is on the center of my back, and my hands are pulling the bar down (though not forcibly), as opposed to holding it up.
I've added a picture of me fucking up next to a grab from the DVD of a guy holding the bar perfectly. The picture angles make it a bit confusing, but if you look at my elbows and compare them to his, you can get a good idea of what is going on.
Attachment 1409
I hope this helps.