Xcode 6.4 does not start on OS X 10.10.5 Yosemite As of this morning, Xcode 6.4 stopped launching on my Mac running OS X 10.10.5 Yosemite.

I tried to launch with

sudo open --new /Applications/Xcode.app


but got

LSOpenURLsWithRole() failed with error -10810 for the file /Applications/Xcode.app


I've reinstalled Xcode, but get the same result. I've tried Disk Utility and antivirus software and my system seems to be clean. 

Any ideas how I should proceed, short of reinstalling OS X?
Make a new user account (admin role) and log out.

If you can start Xcode from Launchpad or Finder in the new account - it's a user level issue. If not, then start with system issues like restart / reinstall latest combo updater or safe boot.