Paypal Standart redirects to Paypal express

[armadillo]

Hello, i have a problem with paypal payment, all was good yesterday but now when i check why payment stops, i saw the paypal is not working.

 

In my business paypal account setup, payment solution is choosed as Website Payments Standard

And in prestashop BO it paypal is set to again : Website Payments Standard 

 

When i try to make payment by paypal it redirects to https://www.mydomain.com/modules/paypal/express_checkout/payment.php

with 

 

"Error 500 - Internal Server Error

An error was encountered while processing your request. Typically this is a temporary condition. Please contact the web site owner for further assistance."

 

I look for many forums but can not find any solution.

 

Thanks