Advanced Guestbook 2.2 admin problem

Every time I get to the admin page it throws me back to the 'enter password' window. This happens whichever submenu on the admin page I try.
Please advise.
Also, if I upgrade to the latest version will I lose the existing guestbook entries?
76 yr old geek

Have a look at http://www.carbonize.co.uk/AG/

Tried the Login exploit fix but it made no difference. I still get the 'loop' problem. I have managed to reset the user and password and itopens the
admin window but still get looped back to the loging window.
Basically I need to alter the email address to which copies of the gbook entries are sent as I want to change my ISP. If it helps here is the site:
www.keithbryant.co.uk
Thanks anyway.