Xcode Cannot Run on the Selected Destination

Question

I was running my app this morning and now all of a sudden I am getting the following error when I try to run on the iPhone 5.1 simulator.

Cannot run on the selected

Answer 1

in addition to deleting all the files in this directory Users/your_usr_name/Library/Developer/Xcode/DerivedData/

i restarted my mac and it worked fine (restarting xcode and the simulator didn't cut it for me)