So many people are suggesting things he has already tried. read the thread before you post.

Knock the center out of the locking lug, and drill out the stud. I have removed several screwed up lug nuts this way. Start with a new 1/8" bit at the center of the stud and drill all the way through the stud. Then step up to 1/4" drill bit, again drilling all the way through, then use a 3/8" bit, drill all the way through. If your still centered on the stud, hit it with a 7/16 or a 1/2" drill bit. At some point, the nut will fall off.

When you get it apart, be sure to check the condition of the other studs, if 1 failed, the others can't be much better. Fix the problem before you get to do this with all the lug nuts. Gene