Here is the screenshot typed and translated:
(After re-registrating my Adobe ID as you told me I get the message:)
Download not possible
Error when calling the license. Licence server communication error:
E_LIC_ALREADY_FULFILLED_BY_ANOTHER_USER
Is that (1) when you download from web to computer (ADE), or (2) from computer to device.
If (1), web to computer, is this a book you have already downloaded and read before?
If so, you were probably authorized with your other ID at the time, so the book is now authorized with that other ID.
if (2), computer to device, and assuming you can read the book on computer,
did you go through the reregister device above ...
To change the ID on a device connected to ADE: use ctrl-shift-E to ADE while device connected to unregister it (cmd-shift-E on Mac); then register again (Help/Authorize Device)
Alles guete