URL Not Found (CodeIgniter App on Amazon EC2)
http://httpd.apache.org/docs/2.0/mod/core.html#allowoverride
If AllowOverride is set to None, the .htaccess file is completely ignored. As such, index.php will not be rewritten. Try setting form_open to form_open('index.php/search'); to confirm.
Edit httpd.conf and change AllowOverride None to AllowOverride All and restart httpd.
Also, FYI, you aren't redirecting to search_page3.php, you are loading a particular view based on a set of conditions. When you say "redirect", I look for redirect('somepage');.