cep.. also be carefull when shooting.. if the palm of your hand is hitting the silver tabs it wont fire either.. then all of a sudden it goes off.. WHY? those freakin tabs.
When rotating the back, it has to clicked in place to fire properly.
Try the WD like I told you.. you can even put a couple drops between the plates so they rotate a bit easier. When rotating stop it half way.. you'll notice the spring clips taht ride the rails of the plates.. that is where you cna put a tiny amt of WD on each side ot the clip. Now play it a few times to work it in and it should feel better n also click in easier too.
The right thing to do is to split the plates n clean out the old grease n put new. You'd be surprised how much gunk is in there.