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
if you have already developed project and you used xib to develop views then
X-Code > Inspector Selector Bar > Interface Builder Document > opens in > and change from Xcode Default(5.o) to Xcode 4.6 .
Build and Run your app it will run successfully, if it won't run again then, header over to iOS Simulator - Reset Content and Settings. delete old app from simulator then Run again.