I just updated to the most recent Mac OS (OS X El Capitan) and went to work as usual. Clicking an image in Lightroom and clicking "edit image in Photoshop CC" edited then went to save it and an odd prompt appeared saying "unable to save file because write access was not granted."
That means that disk or directory permissions are messed up in the place you tried to save. You need to fix the permissions in that location.
(and yes, MacOS upgrades do mess up permissions a little too often)