I CAN'T JOIN IN A SERVER

Hello, my friend has created a server to play. When I open it to join in the page refresh and I can't enter in. We don't know what could be the problem. We are using hamachi to connect us. And other friend can play so I think it is a problem of my computer.

Disable the Firewall or you friend mus add you ip to the whitlist :)

I have the same problem with a friend, what is the whitlist?

I tried what they told me but It still does not work.