I’ve posted about this error before, however, the solution only solved one of the scenarios which causes this error.
The second one, is when you have already switched from Device to emulator and yet you still get this build time error.
This is a bug in Xamarin’s current release (July 2015) and from what I can gather it’s a flaw specific to the VS T4 template for Xamarin.Forms, but I haven’t tried every template so it may be that you run into this with different projects.
The problem is that the generated project file for IOS declares an Entitlement.plist for the emulator target, which is wrong. This should only exist for the Device target.
Open up your .csproj project file and REMOVE the following line under any iPhoneSimulator configuration (there should be one for debug and for one release):
Save your project file and reload it. Make sure your target is on any simulator, not Device, and the error should be gone.
This fix has been requested so hopefully they’ll add it to the next updates.