You may have experienced error messages when accessing videos either directly from a link, or via the Gallery page. Your media player may start to load and then give you a message that the source file is not supported.
The cause of this is due to a sharing of information between your web browser and the media player program. Specifically, a cookie is set when you login that shows you are a registered user. If you don't check the "remember me" box when you log in, then the cookie doesn't get set.
So the solution is to check the "remember me" box at login and the video should play without error.