ATM Posting Rejected

["Keith Taylor" <keith.h.taylor@worldnet.att.net>]

I recently tried to reply to a posting on the ATM list, and it was
returned to me with the following message:

"You are not allowed to post to this mailing list, and your message has
been automatically rejected."

Have I commited some breach of the rules? I find it a bit troubling to
be a member of the ATM list, and then be told that I am not allowed to
post? At least if I have broken some cardinal rule of list manners, I
should have been notified?
Or...is this a problem with starting up the new server? Has anyone else
recieved this message?
Sincerely Keith  (and a bit baffled?)