you would have to ask wp… the nonces are theirs and they have a limited life (few hours)…
not sure I understand the pause question… what do you want to pause?
Andy was saying that if you have been sitting on a page for a long time (overnight or while you ate dinner), the wp nonce may have expired hence the message… if you are saying you just get it between two subsequent page loads or actions, then something odd would be happening…
do you have any custom login plugins or actions? do you run any kind of security plugin? what about mod_security on your server? any caching?
how long has the forum been going? a full reinstall would of course wipe any existing data…