sounds like a broken shift fork (or something equivalent, i am thing in terms of a car transmission), but i could be wrong. if you need to start it, hold the shifter between gears, this will disengage the clutch and then you could use the rope start. I advise you pull the engine from the trike and open it up. if something is broken, i would not ride it too much because i would be afraid of pieces that may have broken off getting lodged into places that can cause more damage. I know there are users on here that can help you more than i can.
Currently owned:
1987 250es
1985 250es (parts)
1985 250es (parts)
1983 200e (parts)
1980 CT70
1995 Foreman 400
1971 AT1 125
1976 KZ400D