ADE won't let me deauthorize my account

I can't load ebooks from ADE to my Nook.  I have tried a bunch of different things.  I am now trying to deauthorize my account to see if that allows me to remove the library card that somehow is attached to the account.  However, when I try to deathorize i get a message asking for a vendor id and password.  I do not know what to put in there.  My library has told me that they don't have a vendor log in and I have tried my own and it won't take it.  I am beyond frustrated.  I have been trying to fix this issue for months, and no one can help me!!