Sorry to be thick here, but you are referring to the bolt that the break lever (the one you grab) pivots on correct? Are you unable to get the nut off? Worst case scenario, if it is this one, can you cut it off with a hack saw, or if you are fortunate enough to own one, a Dremel with a cut off wheel? Pics would help a ton in knowing what you are up against if you can get them.
Brandon