When reassembling, I found an unknown, small black plastic piece on my work surface. It wasn't anything that I'd removed in any step. It had a curved section and a small tab, the whole thing was less that 1/4". Nothing in any of the instructions mentions it.
I finally figured out it was supposed to go just to the right (while looking at the open back of the screen unit) of the hole where the camera fits. The semi circle hugs the side of the camera when you reinstall.
This had me going nuts for about 30 minutes. Hopefully this info can help you avoid that.