9.2.16: Know that Apple has a long standing nasty habit of releasing updates for tools before updating the backend/iTunes Connect (left/right hand fail), so if you updated to the current El Capitan OS X 10.11.6 (15G1004), you'll need to wait (or revert your OS) until the intern shows up for work and sets the flag on the backend to bless it for the public. Est. 24 ~ 48 hours.
As well, the GM version of Xcode 7.3.1 (7D1012) is basically a beta and not allowed for building to submit to the store. Download the release version from the MAS. If you check Xcode/About, you should be using Version 7.3.1 (7D1014).
3.26.19 edit: Apple still makes a practice of releasing new Xcodes before resetting the flags on the backend. Yes it's a problem, no, we don't know why they do it this way. Give it bit, then try again.
6.15.19 edit: Nothing has changed...see above.
9.12.19 edit: Xcode 11 GM is out, and still no change to the above.