I am having problems with an empty application. I have simply created a new "Xamarin.Forms Shared" application in Visual Studio, compiled it and run it against the "iPhone 4S iOS 7.0" emulator and it fails to load correctly. If I run the same against the "iPhone 4S iOS 8.0" emulator, it runs fine.
One thing I did upon creation of the project was to update the nuget references which in turn updated the Xamarin.Forms version. Other than that, this is the standard application template.
According to Xamarin Studio, everything on the Mac is up to date; similarly, everything on the PC is also up to date (the latest updates were installed on both today).