This is a main problem, I suffered many times in my Opencart website. this problem may occurs due to CURL function, this function might be disabled because of some security issue. which is done at the hosting side. you can contact your hosting service provider to enable the CURL function.

Otherwise outgoing port of your web server might be disabled by hosting service provider, because your site might be used extra server resources. Usually this happens due to login into admin numerous of times by attacker. Which is called brute force login attack.