Have new computer but cannot authorize it for ADE as my profile has been used to authorize another

How can I authorize my new computer??? Says easy. But when giving my ADE id it says that cannot authorize any new devices with profile used to authorize any other device. And cannot create new id as already exists! So when I connect my KOBO reader I can download the purchased book, but not allowed to read it. I can however read it on the laptop!!!!!! the new one. Feels very confusing.