What is this pain in my forearm?

I have been weight training for a year now. I do a lot of straight barbell curls for my biceps, however every so often I get a terrible pain the back of my forearms. The pain makes me need to take days off of lifting. I would not care if I just stopped hitting the biceps for a while, but it is painfull to do just about any workout. It is not my forearm strength. Am I using the wrong form for the curls or what? Any helpful answers would be great. Thank you.