Digital Editions Won't Authorize

I downloaded ADE three days ago on three devices: my MacBook Pro, iPad, and iPhone. Since then, I've been receiving the error listed in this thread on all three whenever I try to activate the app or load any books into it.

That thread suggests updating to version 4.5.11, but the most recent version I've been able to find, which I'm running on my MacBook Pro, is 4.5.10. Meanwhile, the two iOS devices are running the most recent updates and still getting the error.

How do I get this app to work?