Are you trying to get the nut off the shaft? If so, you might want to try an impact wrench. Just give it a quick jolt at the low setting on the impact wrench and it should pop it loose. Don't know if you have a right or left hand thread on the nut, so don't over do it and strip the threads on the shaft or nut.
I had the same situation on a Porter Cable router trying to get the adapter off the bottom that holds the collet. One quick jolt and the adapter was in my hand.
Just something you might want to try at your own risk of course.