Dean,
I have experienced exactly the same issue as Scott - once I read the results once and log out, I cannot log back into the results anymore.
I type my password and hit the login button and nothing happens.
I thought it was cookie related as I deleted a "Listmail Administrator" cookie and was then able to login. Once I logged out from that session, I was again no longer able to log in at all (and the cookie I deleted was not rewritten to my cookies folder).
I then changed my cookie settings to allow all cookies and still was not able to log in - seemingly killing the cookie theory.
I can still access my Listmail install, just not this new read tool.
Any suggestions would be great - this is an awesome tool and something I definitely want to use.
Cheers,
Matt.