I'm trying to get usb sound working but i get this error :

ALSA lib conf.c:2852:(snd_config_hook_load) cannot access file /usr/share/alsa/cards/aliases.conf
ALSA lib pcm.c:2014:(snd_pcm_open_conf) Invalid type for PCM default definition                                                                                        (id: default, value: cards.pcm.default)

What's wrong?
Aliases.conf is not on my system... but i installed alsa-libs and alsa utils.