Digital Editions - Unable to download

I have previously been able to successfully down load books to Digital Editions but now I am getting the error message below every time I try and download a book. I have tried to get books from different sources and so I'm confident the issue is with Digital Editions. I have tried reinstalling Digital Editions but this has not solved the problem.

Error getting License. License Server Communication Problem:

E_AUTH_BAD_DEVICE_KEY_OR_PKCS12