I want to run my app on both simulators ios6 and ios7. I'm trying to install ios 6 simulator but I am getting this error:
Failed to install "iOS 6.1 Simulator"
An unknown error occured. Please try again later.
I restarted XCode but not working stil..
Try to reset iOS 6.1 simulator from menu "iOS Simulator -> Reset Content and Settings...",
then run your app in XCode. This helped me.