Adobe ID/password not accepted. a "no permission to copy book to ereader." The "help" section asks me enter my adobe ID & password, which I do, but keep getting a message telling me it's wrong - it isn't

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Can't download books from library onto my e reader.   Get a message reading "No permission to copy book to e reader" .   "Help" section tells me to authorize my computer.  It sends me to window asking for my log in to Adobe.  This window won't accept my ID or password although it works for my adobe sign in otherwise.  I've given a different email and password also set up with Adobe and still it doesn't work.  

Very frustrating!!  What's the problem and how is it fixed??

Thank you.

DM