[Urgent] Can't buy item with payment issue

Hello,

I’m trying to buy an item in themeforest. But, when I checkout with paypal I get this message:

Access Denied

You don’t have permission to access "http://www.paypal.com/webscr?" on this server.
Reference #18.6ccd4c17.1448976729.fd0ed20

What happened? Envato please solve it.

Thanks.