A little more info - year? M16 / T16 might help a bit.
Might sound silly, but where is reverse: left and forward or right and back?
If left and forward its an LT77. Difficulty engaging - does it graunch when you are trying to get 2nd? Does double declutching help?
A couple of quick choices here: either clutch master cylinder on the way out (does it sometimes creep forward if stopped in gear with clutch depressed?), or the synchro on 2nd is going (had that problem with an LT77 in a Discovery - a not unknown fault, but not common).
Cheers,
