Custom Structure permalinks error 404

i have changed the wordpress custom structure permalink to /%post_id%/%postname%/ and get this error :

404 Not Found
The requested URL /mysite/blog/1/hello-world/ was not found on this server.

• wordpress version 3.1.7
• site address: localhost/mysite/blog

i’v changed this function in misc.php and saw the error again!

function got_mod_rewrite() {
    //$got_rewrite = apache_mod_loaded('mod_rewrite', true); //old line with false negative;
    $got_rewrite = true;//force the response to true as we know mod_rewite is installed;
    return apply_filters('got_rewrite', $got_rewrite);
}