Do what I did. Flatten the tab washer off, try to un do the nut with a huge torque wrench and fail. Ride the bike to my mates house who has a torque gun and find the nut comes off in his fingers!! The heat and vibration must have loosened it off. I promptly shat myself.
Providing you immobilise the rear wheel so it doesn't spin you should be able to remove the front sprocket nut without too much bother. If you have access to air tools and a compressor it makes it much easier! Just make sure that you torque the nut to 125 Nm once you have fitted the new sprocket.
Tool the wheel off and went over to the local motorbike shop. ?5 in the tea fund pot and sprocket was off.... (i could hear the torque gun in the background whilst the manager was trying to sell me a new R1