I am running Beta 6 and 2.1 still... Before I launch the app, I have been deleting the E:\TDATA\ and E:\UDATA temp folder that XBMP creates. Supposedly you have to do this when switching versions, to make sure "no wires get crossed".
This has been working a little better for me, but I still have tons of problems with 2.1. Most MP3's are flakey, and almost all my divx movies have problems. (These are movies that I compiled myself with the divx5 codec and mp3 audio... They are perfect files, and play great on Beta 6.) Even some of the downloaded movies that I have tried don't work well... The movies start, but at some point it just exits back to the menu. Or it just freezes when trying to start the avi...
I still don't like the aesthetics of 2.1, but I wouldn't mind so much if it worked a little better... Can't complain too much though! It was free, and still in development...