I have seen this error before. When loggin in to my phpBB forum for my intranet I am given a 'page not found' error. However, if I hit 'back' and refresh, i am logged in. I had the same problem with another
board I run. And to fix that problem, the server name was set to 'www.wormwoodchronicles.com' and the cookie domainw as left blank. Setting the cookie domain to '.wormwoodchronicles.com' fixed the issue.
With this intranet board I have both server name and cookie domain set to '127.0.0.1' and i get the problems. I don't know what would be the correct setting on this.
Hopefully someone can help with this.. thanks in advance.