When trying to load a file into Mplayer using the Load File dialogue, several of the leading characters in the filename are replaced with garbage characters. For example, master.avi would show as something like (*)&ster.avi. Needless to say, the file will not be found. Mplayer will work if the filename is specified in the console command. See website above for screenshot.
This may well be an upstream error
Try pre5, thanks.