Mailman admin saying "Error decoding authorization cookie"

[Alan Chandler <alan@chandlerfamily.org.uk>]

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I suddenly seem to have a problem with 
mailman

After successfully logging in to admin one of my lists (all lists show this 
problem) - if I select another subsection I get thrown back to the login 
screen with the text

Error decoding authorization cookie

shown in red at the top of the screen.  

I haven't made any changes in this area recently other than dselect update 
(debian woody).

I am using konqueror and cookies are enabled.

Any ideas what might be wrong - or how to go about debugging the problem.  
I'm stumped.
- -- 

  Alan - alan@chandlerfamily.org.uk
http://www.chandlerfamily.org.uk
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