the way to solve the error you've given is to edit the alsa configuration to allow multiple connections by external programs. I thought this had become a default on newer distro's but maybe not.
open the alsa config file, possibly /etc/asound.conf or similar. and in there should be a declaration o this "default" server. This might not be quite right for you, so google could help you with some alternative configurations, but my setup is:
to be honest, i don't understand each part, and from what i read this is actually overkill... you *might* not even need the second part at all and let dmixer run on what i expect are suitable default settings, but essentially it's the use of the "dmixer" plugin.
BUT... if you're using kde or gnome, you'll probably have a higer level sound server running already on top of alsa, and although they suck, it might be easier to make sue you've tried using both ESD and ARTS outputs instead of alsa.