Follow these steps:
sudo /etc/init.d/alsa-utils stop
sudo alsa force-reload
sudo /etc/init.d/alsa-utils start
When I was running openSUSE 11.1 in previous decade, sometimes the ALSA sound diver throws an error while playing some video with VLC media player. The solution was, just to restart the ALSA sound driver by running the following command as super-user:
/etc/init.d/alsasound restart
