A few months ago,I have bought a Kobo Aura One for my wife. To allow me the possibility of buying E-Books on multipled E-books shops, I have installed ADE. Everything worked fine.
Yesterday, I bought a second Kobo Aura One for myself. There were no problems to load the E-Books that I already had in my Kobo Account, as this doen't involve ADE.
But when I asked ADE to autorise this second Kobo Aura one, I got the error message E-ADEPT-USER-UNKNOWN.
Thank you to everybody who could help.
I think that you authorized the books with a different Adobe ID than the one used on the first Kobo.