You are making an error in thinking you have an account at Nabble. See:
http://greghelp.991552.n3.nabble.com/My-Nabble-Account-Why-That-s-Wrong-Thinking-tp4012787.html
j.e.collins wrote
I have been administering the Power TAC Developers account for at least 9 years. A couple days ago I tried to respond to a post and discovered that my account is gone -- I can no longer log in, and I cannot even get a password reset because it says it does not recognize my email address. So I created a new account under my gmail identity in order to post this message. I would prefer not to put my primary email in this message for obvious reasons, but the username on the missing account is "grampajohn".
I take it that you refer to the forum at:
http://power-tac-developers.975333.n3.nabble.com/Go there. Follow the "People" link and on the following screen filter the list of users to show only "Administrators". Grampajohn is listed there. Click on that user and on the next screen there's a link there to send that user an email. It should come to you at the address at which you are registered.
My best guess is that you normally stay logged in and have either logged out or are using a different machine to normal to attempt to post and - again guessing - that you use a old email address on that forum and you assume that you changed it a while back - but in reality have not.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.