Same with me. I got forearm splints from doing heavy straight bar curls. Especially on preacher curls. It sucks and i thought i'd have to wait ages for bone to heal but there is no need to wait if you just change to hammer curls using DBs or a tricep bar.
EZ bars are also alright for me if i keep it light.
It seems to be caused by some people's bones being different proportions and difference in joint structure (veey minimal however) which causes supinating to cause a lot of shear force on the ulna. Hammer curls and rows are great for biceps anyhow.
I also increased calcium intake to be sure.