Stuck in first..

[wzc0014]

When I park my bike I leave it in first. Upon start up I throw it in neutral. But, lately it has become very difficult to get it into neutral - to the point where I have had to lean over and lift up the lever by hand. Doesn't happen every time, but very often. Also sometimes when shifting down from 2nd, it will get stuck in neutral on the way down and is hard to get into 1st. This happens less often than getting stuck in first when parked. I never have any trouble shifting up when riding, and only occasionally on the downshift to first at a stop. Anyone know what could be causing this and/or a resolution?