The original question was:
"why am i being told that my device can not be authencated? i then am not
allowed to download a book"
You've not given us the actual message text, so there are a couple of
possibilities here. The answer Jeff Wright gave you assumes that ADE does
not see the device, but another interpretation of your question would be
that ADE is telling you that it sees the ereader, but it's not able to use
it because ADE cannot authenticate it.
The last part usually means that you bought the ereader, but you haven't
registered it with the manufacturer or distributor (SONY, B&N, KOBO, etc.)
If that's the case, then you can go to that website and do it. The process
usually asks for you to supply an ID and password, and it makes things MUCH
easier down the road if you use your Adobe ID and password.
Hope this helps!