[_ck_]

This happens because there was a bug in early bbPress 1.0 alpha where it does not handle a blank query OR your HTACCESS file is missing a way to handle empty topics names.

Edit your .htaccess file and add these two rules to the bottom of the rule list (before </ifmodule>)

RewriteRule ^topic(|/)$ /forums/ [R=302,L,QSA]

RewriteRule ^forum(|/)$ /forums/ [R=302,L,QSA]

Note that you have to change /forums/ to the base of your forum path, whatever it might be if it’s not forums. ie. /discussions/

/community/

whatever, etc.