Sorry, I hadn't noticed you had said Mac on your first post, so the possible Windows bug was a bit of a red herring.
Just to clarify: is the problem
- getting the book onto ADE/Mac; you can't open the .acsm file even on the Mac
- you can't copy .epub file from ADE to Nook
- you get the .epub file to the Nook, but can't read it there.
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One possible reason is a bug in ADE 2.0/2.0.1 that means it won't work with library books on certain devices; in my case a Sony PRS-350.
The ADE2/Sony combination works on other books, and ADE2 can read library books when the Sony isn't plugged in,
but plug the Sony in and you can't transfer library books to the Sony, or even read them on ADE.
The solution to that (and to many other problems people have had on this forum) is to replace the junk called ADE2.0/2.0.1 with v1.7.2
~~~~~~~~~ There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2. (You can have them both installed at once if you like.) Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac. http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172 Some people have found ADE trying to upgrade automatically. It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run. Probably best to say no if 2.0.x installation asks if you want to migrate your library.