I put in a ticket at Katastrophos, but I thought I'd repeat it here.
If a directory name contains a percent sign, "%", all files in that directory are not read. The file is added to the playlist, but the entry is empty, ie, there's a line for it, but it's blank. As a result, mplayer returns an error when called to play that file.
I had a directory named "100%Dance", because that's the album name. It took me a bit to figure out why the songs (ripped as ogg/vorbis if that matters) didn't show up in the playlist, but took up space. Once I renamed that directory to "100pctDance" everything loaded fine.
It's easy to work around, but I thought I'd post it. It's the 0.9 Cacko version.
Excellent player. Thanks again!
Asterix