you might have tendinitis on that arm
When I do curls with a straight or EZ bar I get a sharp pain in the area circled in the picture.
/i.imgur.com/a2LvI.jpg (not enough posts for link)
It doesn't hurt when I do DB curls, also I feel nothing in my left forearm, just the right. It also hurts in the rack chin position. I can work through it for weeks but than it catches up with me and becomes very sharp pain. Maybe it's a ligament problem or something?