Error message 'Unable to Download: Error getting license'

Hi, 

I've paid for a bunch of textbooks. The third party cites - like Cambridge publishing etc - tell me to download Adobe Digital Editions. When I try open the ePub files or whatever format the books are in, Digital Editions comes up with the error message 'Unable to Download. Error Getting Licence. License Server Communication Problem' 

I tried calling customer support. A useless man forwarded me to someone in a photography department who didn't know anything about Digital Editions. I tried the chatbox, and the human assistant said Digital Editions wasn't their forte. Adobe sucks. 

When I've googled, it says to authorise myself. Seemingly, there is an old email associated with my Digital Editions. I can't 'unauthorise' it, because I don't know my Vendor ID, whatever that is. 

I just need to be able to read the textbooks I've paid for.