I hit the upgrade to WP 4.2.1, having migrated to DreamPress today, and the upgrade came out while doing some cleanup.
Now, I get this: No Update Required
Your WordPress database is already up-to-date!
With a "Continue" button. Hit the button, I'm redirected to my website front page. So I cannot log into my admin, at all.
Via this post - http://wpguide.org/fix-no-update-required/