I recently updated my development environment to 4.2.4 Build 35 and I can no longer build our solution. Xamarin Studio fails with an error that states:
Build failed. Could not find type 'System.Globalization.SortVersion'.
This happens when it tries to build or clean the very first project in the dependency tree in the Solution.
I upgraded to 4.2.5 Build 0 this morning and the problem is still there. Tried on multiple machines with multiple OSes (Win7 and Win8) and the failure continues, so it's not an environment problem.
It's definitely a problem in Studio, as the build server, which uses gmcs through Jenkins continues to build the solution without any problem.
Rolling back to 4.2.3 Build 60 eliminates the error.