Swift: Thread 1 signal SIGABRT

Question

After upgrading Xcode from 5 to 6 beta, almost every project gives me an unexpected error after running the application. There are some other posts with this title but the error

Answer 1

This error is caused when you have 2 or more of the same IBOutlets or IBActions in your main.storyboard inspector (right arrow key at the very end of your options). Find out where there is double, and delete the one you don't need! It should work perfectly fine after that.