authorize the computer

I downloaded ADE, I borrowed some e- books from the library and I can see them in my ADE.. BUT I can´t save them in my Letto when I connect it to the computer.

Computer says : authorize the compuer, enter your Adobe ID, and I do that.

The answer is : incorrect user ID or password for the selected ebook vendor. Pleas try again.

Pleas help me, and I am not very used to computers so I appreciate step-by-step help.