This is the error I get every time I start my system. I have just upgraded from Ubuntu 15.10 to 16.04 around a week ago.
UPDATED original response was incomplete
I had the same issue, you have to purge qemu-system-common. There is a left over config file. If you don't want to purge your qemu config files, you can let it sit around for a little longer. Next release in October will probably clear up this issue.
sudo apt-get purge qemu-system-common