Adobe Digital Editions problems with authorization and reading a book

I am having a problem in Adobe Digital Editions. I have no problems authorizing my computer with my Adobe ID and login. However, when I attempt to read a book, I receive the message that the computer needs to be authorized with a vendor ID to read the book. When I select “continue,” I receive the message the vendor account I entered is not associated with the item I am trying to open. I have read books previously using my Adobe ID to authorize my computer and have not had a problem or these messages. Does anyone know how to fix this?