A few minutes ago, I merely pressed/clicked the back/arrow button to my internet web browser after verifying my Twitter account via my public profile of Gravatar and got the following error message from the Twitter site:
The request token for this page is invalid. It may have already been used, or expired because it is too old. Please go back to the site or application that sent you here and try again; it was probably just a mistake.
You can revoke access to any application at any time from the Applications tab of your Settings page.