Help with Digital Editions

Hello,

I installed adobe digital editions on my new computer, however I get an error message when trying to transfer a library book from there to my nook.  When downloading, it has asked for an Adobe ID and I did not think I had one and thought they were asking if the new computer would be the only one I would be using digital editions on.  I misunderstood their question.  I have uninstalled and tried again with both editions and still get the error that I am not authorized to transfer.

Please help!  I just got this computer and plan on having it for a few years so need to be able to transfer books with it!  Thank you!