Using Xcode 5 GM, anytime I switch to the 5.1, 6.0 or 6.1 simulators to test, I get the error \"iOS Simulator failed to install application.\" When I reset the simulator it
Alternatively, header over to iOS Simulator - Reset Content and Settings.
This can be easier when you have a lot of apps on the simulator and can't remember which one you're currently working on.
You need to do this for every iOS Simulator version that causes the problem.