Can't open ebook on second PC

I have a customer that is trying to authorize/activate Digital Editions on two PC's with the same account. The ebook works on one of those computers but not the second. The Digital Editions on both computers have the same account, but when I try and open the book on the second PC, I get the following error:

Error getting License. License Server Communication Problem:

E_LIC_ALREADY_FULFILLE_BY_ANOTHER_USER

The first computer had this problem when first activating the ebook, but then we decided to come back the next day and continue looking at it. But when we came back the next day, it started working without us doing anything, so I can't replicate the results.

I've tried uninstalling, reinstalling, deactivating, reactivating. I'm not sure what to do at this point. Thoughts?