Mercadopago module

[Fabián]

Hi, I´ve been working with Prestashop 1.6.1.17 and I am struggling with the classic Mercadopago checkout problem. When I reach the checkout my payment method "Mercadopago" doesn´t show.
(Mercadopago is a module that allows you to sell products online. Since It´s very popular and the clients can pay you in many ways, I think it´s the most important payment method here in Argentina. 
I´ve noticed that in the Modules->Payment section Mercadopago isn´t included in "Active payments modules". I´ve notice also that I don´t have a checkbox in the section "currency restrictions", I have 2 hyphens instead (--).
I´ve tried modifying the mercadopago.php file (located in /public_html/modules/mercadopago ) replacing the word "radio" by the word "checkbox" . Even though this modification affects the currency restrictions section , putting a checked checkbox instead of 2 hyphens, the module still doesn´t appear in "active payment modules" section. I´ve pressed the button "Save restrictions" but my checkbox dissapear and the 2 hyphens come back. 
I can´t find any solution. 

Does someone know what may be the problem?

There´s also a non free version of Mercadopago ¿Someone has tried the pay module?

Thanks in advance.