Make certain you upgrade mono for Ubuntu first.
See notes here Ubuntu
Here are command lines, in this order.
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo “deb Index of /repo/debian wheezy main” | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install mono-devel
sudo apt-get install mono-complete