DRM authorisation

I have purchased an E-Book with DRM authorisation, and have installed Adobe Digital Editions after which I have authorized my computer and my e-reader. I can download the E-book from the website and put it on my E-reader, but when I try to open the E-book on the E-reader it says that the book is DRM protected and I have not authorized the E-reader. I can not read the book now because it won't open. How can I solve this?