How many miles on the bike? It should just slide off but if it's not, it's being held up by something. How do the ends of the splines look on the main shaft? Was there a washer between the clutch hub and hub nut? If not, maybe the splines are mashed up. You will have to take a small file and clean the shaft up. That bikes and '05 so it probably has an old style main shaft in it anyhow unless you replaced it already. The bearings in the transmission bad? You have any play on the shaft?