Is this a Nook dedicated eReader or a tablet?
If a tablet, which software app are using to read books? (eg Bluefire, one that came with the Nook, ...?)
Copy the .epub or .pdf file, not the .acsm.
Usually, the important file is the .epub file (or .pdf file) that contains the book contents.
The .acsm file is just a token that enables download of an appropriate DRM .epub/.pdf file.
ADE automatically processes the .acsm to download the real file: after that the .acsm is pretty irrelevant.
If a dedicated eReader, did you use ADE to transfer the file, or did you copy it across using file manager?
If you use ADE to do the transfer, it will automatically transfer the .epub/.pdf, not the .acsm.
Have you registered the Nook with Adobe.
If an eReader, register it from ADE with te Nook plugged in.
If the registration goes wrong, deregister the eReader (ctrl-shift-E while plugged into ADE), reastart ADE, and reregister the eReader.
If a tablet, you probably need to register it using the ebook reading app (Bluefire etc as above).
