How are you sideloading?
That sounds like an Adobe message rather than an operating system message. I think of 'sideloading' as copying the file outside the ADE environment; eg using a file manager such as Windows Explorer. I would expect that to work regardless of DRM permissions; though if the DRM wasn't right it would then fail when you tried to read the file on the Nook.
If you mean using ADE to transfer to the Nook, are you sure the Nook is registered to the same Adobe ID as the computer?
