Ok, after a short time of trying I found the solution of this problem. First rhythmbox sets /MUSIC as the path to the music at a PSP. Second someone (also rhythmbox??) adds the entry from hal to this path (this entry is "PSP/MUSIC"). At the end rhythmbox tries to find the music at "MUSIC/PSP/MUSIC/" which is more than wrong. I just set the entry in hal ("/usr/share/hal/fdi/information/10freedesktopusb-music-players.fdi") to "" and now it works fine.
Ok, after a short time of trying I found the solution of this problem. First rhythmbox sets /MUSIC as the path to the music at a PSP. Second someone (also rhythmbox??) adds the entry from hal to this path (this entry is "PSP/MUSIC"). At the end rhythmbox tries to find the music at "MUSIC/PSP/MUSIC/" which is more than wrong. I just set the entry in hal ("/usr/ share/hal/ fdi/information /10freedesktopu sb-music- players. fdi") to "" and now it works fine.