[Mon Jan 27 08:04:06 2014] [alert] [client x.x.x.x] /home/…/public_html/.htaccess: Invalid command ‘Header’,perhaps misspelled or defined by a module not included in the server configuration@H_404_4@

这是我的简单.htaccess：@H_404_4@

<IfModule mod_rewrite.c>
    Options -MultiViews
    PHP_flag display_startup_errors on
    PHP_flag display_errors on
    PHP_flag html_errors on
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^ silex.PHP/ [L]
</IfModule>

可能有什么不对？@H_404_4@