When i try to change the language: Warning: Cannot modify header information...

[tubadc]

Warning: Cannot modify header information - headers already sent by (output started at C:\Program Files\SWsoft\Plesk\admin\plib\locale\messages_pt.php3:1) in C:\Program Files\SWsoft\Plesk\admin\auto_prepend\auth.php3 on line 452

This error appear all the time when i change the language for my own...

How can i fix it?

Tks