paypal and internal server error

[BerghemDeSass]

i've configured paypal on ps but when i try to click on paypal button i get some issue:

 

500 internal server error

 

on server log i see:

 

[Wed Nov 13 15:27:04 2013] [error] [client xxx.xxx..xxx] SoftException in Application.cpp:249: File "website/modules/paypal/express_checkout/payment.php" is writeable by group, referer: website /index.php?id_product=593&controller=product

[Wed Nov 13 15:27:04 2013] [error] [client 194.242.61.3] Premature end of script headers: payment.php, referer:/index.php?id_product=593&controller=product

 

previously there's 777 permission on folder/file

now i changed it to 755 folder and 654 for php files...

 

 

suggestion?