Don't know where to find unlock code

I am trying to open an ebook that I downloaded from barnes & noble to my pc. I get a screen that says:  This computer is not allowed to open......(book Title)..., to open enter info below;   there is one box that asks for user name and the one under that asks for unlock code.  I have tried using my adobe user name and password but they do not work here.  Where can I get the unlock code and do I still use my user name for adobe.?