Well I have had my new Nikon D40 w/18-135mm lens combo for about two weeks and I have used it on about 6 different occasions. Several times now I have found myself having to twist the lens back and forth slightly because I have received a Lens not Seated message on the screen and it wouldnt take pics till I messed with it. Is this common or something I should be worried about? I am 99.99% sure I attached the lens correctly (even tried removing it and reattaching just to make sure) but still get the same message once and a while.