I have installed one free phpbb forum script recently and experience some issues with it! When for example I visit members page to see all the post made by the certain user Not Acceptable error is displayed as a result! The second issue I have is login procedure – a user is required to provide my login/password details twice each time when he/she is logging into the system!

http://www.phpbb.com/community/

This could be a template issue? Do you have a custom template?