Well, I used to have this problem. What I did back then was sudo chmod 777 /dev/snd/seq and it worked. That's because permissions aren't correctly set. However, recently I found a post and added myself to a group...voila no more need for that. The problem is: which group(s) did I add myself to? It was either related to 'audio' or 'pulseaudio'. Maybe a google search might help? Anyway, to check that it really is related to permissions, try to chmod 777 it, please. Be aware of the security risks (it resets itself upon reboot, though)
