fault with my colchester 2000l fanuc OT will not run past startup line

Hi guys hoping someone could shed some little on the problem i have with my colchester 2000l cnc running fanuc OT

Basically machine was in day to day use until yesterday when the machine decided to stop working it doesnt seem to want to run past the first line of the program in cycle it just moves to startup position selects the tool and fires up the spindle but after that it does nothing . Now i can change the start up line position to anywhere and it will move to that position and the same for the tooling it will select any tool you put in the start up line . Now ive been told by a colchester service engineer that it sounds like an encoder problem so ive just driven to colchester and collected another encoder and fitted it up but this has made no difference what so ever . Now im at a total blank and the service engineer has no more ideas either . So im hoping somebody can help me out ?

look forward hearing any ideas people may have

regards adam

check DIAGNOSTIC 800-801, at rest(after move) the following error displayed there must be less than 'in position' parameter stored at PARAMETER 500-501, if not you may need to adjust your drive's 'offset' pots. usually auto drift comp will be active, and it will throw comps in parameter 544(i think anyways), sometimes if a machine sits homed up on a pile of chips or whatnot, the drift comp will throw a bogus value in the 544s and it wont run until corrected.
there is a diagnostic (700?) that shows if waiting for inposition check (CINP?) or other things... some oems used a relay for their FIN signal, if FIN is stuck on, it willl also stick as if in single block or something...