A couple of easy checks,
1, have you had a crash and now your clutch lever won't go out all the way because it hits the bark buster?
2, check if you have clutch clearance? Can you pull the outer of the cable out from the top mounting position? You should be able to move the outer of the cable about 4mm or there Abouts
If both these items are ok then you will have an internal problem possibly like Tim said the clutch plates or the sides of the clutch hub is worn and the plates are locking on it.
Have you drowned it in water the last ride or anything? Water can boil in the plates and desolve the linings.
Let me know and I'll advise you more or feel free to give me a call
But 1+2 are the most comin problems and the easiest to fix aswell.
Cheers Dave
0408136949