Not sure how yours is set up but it's probable a steel bolt in an aluminum bracket. The aluminum has probable corroded and seized it up. If it's in a place that you can heat the aluminum a little to help loosen the corrosion that might help. Caution aluminum melts at a low temp so don't over do it. Worst case you could break off the bolt, drill it out and re-tap to a larger size if needed. All is not loss. Either way you get it off, apply never seize of some sort when you put it back together.
"gene"