Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
The release notes state the following:

Known issue
iCloud Drive may not be correctly enabled on a 2nd device after signing in via Buddy or Settings.

Workaround: Logging out of iCloud, logging back in and enabling iCloud Drive should resolve the issue. In some cases, you may need to try these steps more than once
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.