I installed the MDK (whatever that is??) from the following directory...
http://download.xamarin.com/MonoFrameworkMDK/Macx86/MonoFramework-MDK-3.2.6.macos10.xamarin.x86.pkg
... and that fixed things for me. No need for an uninstall and reinstall of my Xamarin setup.
Note that I had to quit and restart Xamarin Studio for the change to take effect. I also restarted my Mac for good measure!