PayPal Express Checkout redirecting to payment

Hello,

I have created e-shop - https://www.steamids.net. Everything was ok but something went wrong. If my customer wanna buy product and he gonna pay, He is again redirected to > /index.php?main_page=checkout_payment . I will not receive money and order is not placed... Can you help me please?

API Signature -- Username
API Signature -- Password
API Signature -- Signature Code

is set correctly.

So my customer tried to buy product again....

I have seen in "Who is online" that he was redirected to -

/index.php?main_page=checkout_process
then
/index.php?main_page=checkout_payment

// IPN is enabled too and http://steamids.net/ipn_main_handler.php is set correctly!

I using v1.3.9h

Same problem here: http://www.zen-cart.com/forum/showthread.php?t=135271 /// and sry 4 spam but i can't edit