I acquired an aftermarket Bresson focusing screen for my Nikon D5100. I very carefully followed the instructions to remove the old screen. However, I find that I can not get the wire retainer to latch again. I put it behind the latch, it pops out. Before I put my tail between my legs and head for the repair store, can anyone suggest another course of action? I can't even get the latch to stay put with no screen in place at all.