Land Rover Repair: refurbished series 2 gearbox problem, mario mario, shift linkage

Question
HI there ,
i have just refurbished my series 2 gearbox at my mechanic.
when i started the engine for first time i could engage  all gears and drove the landy up a ramp out of the garage on 4 w d , drove about 50 feet on first 2 w d  , 2nd and 3 ,and stopped at a corner.
when i drove again the 2nd gear could not engage any more.
All other gears function ok.
i tried going into 2nd with engine off ,and also tried pushing l r back and forth in free position and on other gears ,no difference.
forks look ok and inspected for any obstructing object.
what is stopping the 2nd gear to engage .???
thanking you in advance  mario

Answer
Mario, with all due respect, I'm not sure what the question for me is here.   If you just assembled the transmission, and it shifted into second gear once and will not do so again . . . what is there but an internal problem?

I assume you are familiar with the simple shift linkage on that vehicle, and it is all working right and free.

If so there is nothing to do but remove the gearbox and see whats wrong inside