my MP3 player plays some .OGG files, but not others. No idea why this happens
Assuming you specifically mean Vorbis, not all players support all quality settings. iAudio G3, for example, doesn't support q-1 or q-2. Some of the iRivers barf when the instantaneous bitrate is below 96Kbps or over 225 Kbps. Sorry for the thread drift.
To the original poster with MP3 woes, do you use constant bitrate or VBR?