Permalink postname not show

i have try custom Permalink (/%pagename%/) only post but show this error

Not Found

The requested URL /index.php was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Apache/2.0.63 (Unix) mod_ssl/2.0.63 OpenSSL/0.9.8e-fips-rhel5 DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 mod_perl/2.0.4 Perl/v5.8.8 Server at phonepedia.net Port 80

please help