"E_LIC_ALREADY_FULFILLED_BY_ANOTHER_USER" error comes when you previously downloaded the book with some authorization credentials in ADE.
Now again if you try to download the book from same download link but current ADE authorization is different, you will receive this error.
1. Make sure ADE is authorized with same credentials, as it was authorized when book was downloaded for the first time.
Then this error will not come.
I have the same issue and lost access to all the books in my library. Your advice does not work. I have followed all instructions on this forum. Where do we get e-mail support?