DTAssetProviderService could not start DTXConnection with Simulator

Killing the simulator and restarting it from Xcode helped me.

You are probably using macOS Sierra which breaks Xcode 7.3.1 (mac store version)

Use Xcode 8 beta or Xcode 7.3.1.dmg downloaded from the Mac Developer portal for a fix https://developer.apple.com/downloads

Direct link to Xcode 7.3.1: http://adcdownload.apple.com/Developer_Tools/Xcode_7.3.1/Xcode_7.3.1.dmg

Yes,It happens after upgrading to Xcode 7.3 and Probably You run first time in a simulator.

When you see this error, Just click "Ok" but Don't quit Simulator or Xcode,Simulator will continue with its process and you can see the progress bar. Let it finish first and then Run project again,You will able to make it run successfully.