Error message

• Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in include_once() (line 334 of /var/www/mountains.ntua.gr/sites/default/settings.php).
• Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in include_once() (line 335 of /var/www/mountains.ntua.gr/sites/default/settings.php).
• Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in include_once() (line 343 of /var/www/mountains.ntua.gr/sites/default/settings.php).
• Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in include_once() (line 350 of /var/www/mountains.ntua.gr/sites/default/settings.php).
• Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in drupal_settings_initialize() (line 819 of /var/www/mountains.ntua.gr/includes/bootstrap.inc).
• Warning: session_name(): Cannot change session name when headers already sent in drupal_settings_initialize() (line 831 of /var/www/mountains.ntua.gr/includes/bootstrap.inc).