Try signing out of the CC desktop app, then sign back in again.
I have the same issue.
I'm on a 27" iMac, with all current updates. It opens fine on my older MacBook Air.
I've tried rebooting, uninstalling, repair permissions, etc all to no avail.
Have you tried signing out and signing back in again (preferences on the CC app).
Jim Wilde, you're my hero!
I'd been QUITTING CC, instead of signing out then in.
All is right in the world!
this worked thanks