But have you ever found that when you tried that, you get:
...even though you KNOW that you're entering the right id? Indeed, one that has been used before?
Perhaps it also happens on other Adobe site properties, and the trick I propose may work for you, also.
Log into another Adobe site pageOne solution I have found is to just log into another Adobe page requiring a login with your Adobe id, like the Adobe CF Forums (or perhaps the download page for CF).
After logging into the forum page, I found I could return to the CF comment page and then login. You may need to refresh the page first (so copy off your comment so it's not lost, as forms fields aren't preserved on refresh in all browsers).
Hope that help someone. Since I had googled and not found anyone else offering an answer, I wanted to share it, though I hope it's something folks rarely need.
PS I'll note that I did try logging in using multiple browsers and even different machines, when I got the error. Nothing worked, so I don't think it's a client-side thing but rather some server-side thing. If anyone has thoughts, feel free to share.