Is there any way one can undo "mark all messages as read", I have numerous times inadvertently hit that instead of next page (another forum I use has the "next page" click in a similar position hence my problem)

Using the "Go back" option doesn't allow one to see the second page after the inadvertent mark all read.

The first thing I'd try is deleting cookies.

Go to 'N  Gauge Forum' Near the bottom under 'Stats' you will find - View the most recent posts on the forum - click on that
and you will find at least 10 pages of messages/posts/answers.

Roger