After 2.5 hours on the phone with Apple last night, I have the solution, and it's incredibly simple: Change your iCloud password. Really...that will fix it. The tech said the password request could be all it needs.
You'll need to go here: https://appleid.apple.com to reset password.
Then you should back-up all you contacts, notes, calendars and documents locally. Then log out and back in to your iCloud account. Restart you computer and you should be back in business.
Sounds simple and stupid, but it fixed the problem for me.
Hope this helps!