I have a few ebooks that my son added to the Sony Reader he bought for me as a present that I can no longer access as the Reader is now authorised under my email and Adobe ID but the original ebooks he purchased are still under his email and Adobe ID so the Reader will no longer open them.
I have access to both his Online eLibrary Account where he purchased the books from, and to his Adobe ID account but can't work out how to reauthorise the books. I contacted an Adobe online technician but he could not help and referred me to this forum.
Unfortunately, your can't reauthorize books ~ one of the many weaknesses of the Adobe DRM infrastructure.
The only solution is DRM stripping. Use a DRM stripper such as epubee.
Authorize a copy of ADE under his ID, DRM strip his books, then reauthorize with your ID.
To deauthorize an already authorized ADE to permit reauthorization, ctrl-shift-D in library view, cmd-shift-D on a Mac.
I do NOT advocate using such code to get around the valid limitations placed on a DRM book.
However, where the problem arises only because of the ineptness of Adobe's ADEPT DRM infrastructure and its implementation,
such a measure is totally justifiable.