"Ebook file protected" error message.

Since downloading Digital Editions and the my new book "The First Stone", my Aurotek Libre e-reader can not any of my previous books or the new one.. I get an "Ebook file protected" error message. I uninstalled and reinstalled, ensured my computer was authorized, and read any trouble shooting I could find and still no luck. It is the .EPUB  files that I cannot open on my e-reader. If I open the Libre file on my PC and choose an e-book it will open but the moment i try on the e-reader I get the error message. Please help.