Do you have error reporting for php turned on and have the level set to E_ALL? It seems that there is a php error that is not being returned to the screen. If I try to visit the link that is listed in the error message you have it shows me a 500 error for the page. If I try to go to the search page I get access denied and I'm sent to the login page. Since the first things at the top of this page should be the include files and the access check it seems that it is not getting that far on the page. My guess is that there is an error before the redirect occurs, this could be from one of the include lines or the generic 'headers already sent' error message. Have you modified this page in any way? Do you have any white space that is outside of the php blocks? I would like to see this page in more detail, please post back with the page in it's current state so that I can take a look. If I can't spot the issue I will open a ticket for you so we can look into this further.
