Why I get this error when I try to open my Xamarin.Mac project "MonoDevelop.MonoMac.XamMac2ProjectFlavor"?

When I try to open my Xamarin.Mac project I receive this error, any ideas?

Error while trying to load the project '/Users/eduardo/Desktop/MyProject/MyProject.MacOs/MyProject.MacOs.csproj': The type initializer for 'MonoDevelop.MonoMac.XamMac2ProjectFlavor' threw an exception.

Solution

I just released that I need to have installed Xamarin.Mac with Visual Studio

Open your Visual Studio for Mac Installer
Make sure that the macOs (Cocoa) option is checked