Mono on MacOSX – “The runtime version supported by this application is unavailable.” v4.5
I have just installed Mono v4.0.4 on MACOSX 10.10.5 Yosemite.
The installer package was: MonoFramework-MDK-4.0.4.4.macos10.xamarin.x86.pkg downloaded from http://www.mono-project.com/download/ last night.