I had the exact same error, and tried everything under the sun, including what was suggested elsewhere on this page. What the problem was for me was that in Keychain Access, the actual Apple WWDR certificate was marked as “Always Trust”. It needed to be “System Defaults”. That goes for your Development and Distribution certificates, too. If any of them are incorrectly set to “Always Trust”, that can apparently cause this problem.
So, in Keychain Access, click on the Apple Worldwide Developer Relations Certificate Authority certificate, select Get Info. Then, expand the Trust settings, and for the combo box for “When using this certificate:”, choose “System Defaults”.
Sigh: for those insistent on downvoting this answer, I am not claiming this to be the only solution for this problem. It’s one solution. It may not work for you. There are multiple reasons for this