Revoking and requesting a new distribution certificate in apple dev center
I had this exact problem just today (Aug 13 2015)

Go into the member center, find the certificate, and revoke it.  Leave the member center.

xcode 6+ will automatically find the certicate has been revoked and will create &amp; download a new one when you carry out an action that requires it.

I sometimes find it also helps to delete your account from Xcode->Preferences->accounts and add it back in.

Indeed it scared me the first time I tried it.