You get the error that fulfilled by another User when the eBook are linked with a other Adobe ID. Often its happens when you open/download a eBook before you authorize Digital Edition. Then authorize and can the eBook no longer read. Has you try to read the eBook without authoirze or download before authorize Digital Edition?
Its possible that I downloaded it before I authorized but the question is: if I uninstalled everything and tried both auhorizing with my adobe ID (i only have one) and without any ID - and it still doesn't work. What can I do?
Is it possible that the license is connected to one certain installation (that I have uninstalled now)?
If you has open it without a authorize you can nothing do. If you have digital Edition is could not open also when you remove it because this empty authoirze is a other as the first. Every what can do is ask his library for reset the ebook so you can starts again with the ebook. Then its can linked with the adobe ID. (You should authoirze digital edition before you open/download a ebook).