Downloading e-pub book

I have a Sony e-reader, model number PRS-600, serial number 14840337 1473535.  I have downloaded an e-pub book from my library to my desktop (Windows 8).  I installed Adobe Digital Editions on my computer.  When I open ADE and drag the e-pub book from my desk top to the e-reader symbol on the ADE screen I get the following message:

Unable to Download

Error getting license.  License server Communications Problem

E_AUTH_BAD_DEVICE_KEY_OR_PKCS12

I don’t know what to do.