Can not upload attached files anymore via Drupal template

Thanks for your quick respons but this is not the solution.

I got the following msg from our provider:
Premature end of script headers: /home/ciqs/public_html/index.php. Here the script.
<?php
// $Id: index.php,v 1.91 2006/12/12 09:32:18 unconed Exp $

/**
* @file
* The PHP page that serves all page requests on a Drupal installation.
*
* The routines here dispatch control to the appropriate handler, which then
* prints the appropriate page.
*/

require_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

$return = menu_execute_active_handler();

// Menu status constants are integers; page content is a string.
if (is_int($return)) {
switch ($return) {
case MENU_NOT_FOUND:
drupal_not_found();
break;
case MENU_ACCESS_DENIED:
drupal_access_denied();
break;
case MENU_SITE_OFFLINE:
drupal_site_offline();
break;
}
}
elseif (isset($return)) {
// Print any value (including an empty string) except NULL or undefined:
print theme('page', $return);

}

drupal_page_footer();

The problem is fixed by cleaning the /tmp file. A lot of statistical data was uploaded in this file and were not removed automaticly. So the /tmp was rather full after 3 years of running.