problem with greek language module

I installed and selected the Greek language as default but when I go change the language back to English through the shop's front page or make an update to the basket then it displays me this error :

("Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\Projects\ecommerce\catalog\language\greek\checkout\cart.php:1) in C:\xampp\htdocs\Projects\ecommerce\system\engine\controller.php on line 27")

and I have to refresh the page in order to complete the action. How can I solve this problem?

ok take a look on my comment on greek module http://www.opencart.com/index.php?route ... sion_id=86