My friend has the exact same problem with the exact same error messages you have, also on FC3. He gave up and is now running mplayer directly from the commandline, which works just fine.
If you can't run gmplayer, note that in the command line version
/ and * keys on numeric keypad raises / lowers volumne.
1 2 3 4 raises / lowers contrast / brightness
and enter starts playing of a videofile.
I. e. if the GUI won't work, do
to play a video file with a gui-less mplayer.