SOMEtimes devfsd doesn't initialize correctly/ontime and the /dev/snd/* doesn't get it's permissions set correctly.
I have noticed that just today. At first I didn't know what the reason was. xmms just complained and a reboot fixed it.
Call me lazy, but it didn't bother me.
Today I got it again, 4th time now and it was starting to get annoying. So i launched it from console, and there it was, permission denied. As root, sound, as user, error. A quick browse through /dev/snd showed me that the audio group wasn't allowed to rw to /dev/snd/*
A restart of devfsd fixed all. If you use fixed nodes then chmod fixes it. If you use devfsd and remember chmodded settings, chmod fixes it. If you use devfsd, edit your devfsd.conf to handle /dev/snd entries properly (make it 0660 and put yerself in the 'audio' group) Dunno yet about the new udev though.