Did you put the right bolts (holding T/box to main G/box) in the right holes.If you put a long bolt in one of the holes meant for a short one it jams something and prevents you engaging reverse. I believe there is something in the latest LRe about it.
Sorry if it all sounds a bit vague, I was only the middleman on the phone between the reconditioner and the customer. We never got another peep out of the customer, and he had been screaming blue murder about warranties until then, so presumably he realised it was his mistake.