Just ran into this issue after installing XCode 5 DP5 and Xamarin Studio 4.19. All existing iOS projects which build in stable Xamarin release now fail to build.
`Building Solution: (Debug|iPhoneSimulator)
Building: (Debug|iPhoneSimulator)
---------------------- Done ----------------------
Build failed. Working copy '/Users//' is too old (format 10, created by Subversion 1.6) Build: 1 error, 0 warnings `