My Galaxy S just started exhibiting this problem. When I take videos with the camera app that ships with the phone (AT&T) I get error messages when I try to playback those videos on the phone. If I try to playback from the Gallery, I get "unable to play video". If I try to playback from within the camera app nothing happens. It does take and store the videos, since I've been able to upload them to Photobucket and watch them on my computer, they just don't play on the phone itself. Any ideas?