To get DRM eBooks into your eReader you must prepare things by
- get an Adobe ID from the Adobe website.
- authorize your copy of ADE (Digital Editions) with that ID.
- authorise your device.
(Active/authorize/authorise/register tend to be used interchangably here).
You can then access books in ADE, copy them to the eReader and read them.
It may be that you haven't done all these steps or that one has gone wrong.
Can you clearify exactly what you have done and at what stage things fail, please?