I finally find the solution:
The only difference I had between the virtual and the real server was that one was behind the nat and the other one wasn’t. So it had to be something with the network configuration! Today I found inside the asterisk configuration the settings for nat. On the real server the nat was on (default value) but it has a public IP so I set it to “public IP”. I then forgot about it because nothing was changing but the reason why it was not working is because I forgot a very important step: restart asterisk service !! So the solution was just to disable the nat in the asterisk configuration…
Finally, after 3 days my user is registered:
h2449554*CLI> sip show registry
Host dnsmgr Username Refresh State Reg.Time
212.117.XX.XX:5060 N 419944XXXXX1 105 Registered Wed, 17 Jun 2015 15:13:11
el_es, thank a lot for your support, really.