Try completely removing any authorization using ctrl-shift-D to ADE (cmd-shift-D if on Mac).
Restart ADE, and then reauthorize with your old Adobe ID.
Don't use your new ID. You won't be able to read DRM books associated with the old ID on it.
Sometimes ADE gets its registration/activation confused and in a semi-authorized state.
Unfortunately, it often then gives misleading error messages about what is wrong. (Adobe forgot the product test part when they release ADE2.0)
A common misleading message is the one that says something like 'this ID is already in use on another computer';
presumably that is the message you saw?