You are a umlaut or special character in your Passwort? If yes change it to only numbers and letters.
I don't know if you read the questions here before you answer, but as I already have written: I have no umlaut or special characters in my password, only letters and numbers and a capital letter.
What you mean with capital letter?
I had a similar problem, but I was trying to log in to OverDrive instead of AdobeID.
I'll just paste the instructions the library sent me
"When you go to authorize computer, you should see some blue writing to the side of the Adobe ID box, which says ‘sign up for an Adobe ID’. Following the instructions will let you create a new Adobe ID which you can then use to attempt authorization."
"If this still does not work, try resetting your Adobe ID’s password."
I created a new Adobe ID and was able to log in with that and then open my DRM ebook just fine.
Overdrive users - turns out I didn't need to log in with Overdrive credentials at all (possibly because my Overdrive account has the same email address associated, I'm not sure - I logged in to overdrive.com to associate the email address, it previously just had my library card number and PIN)