Plutonium

I have played OP GOLD Veteran server on Black ops2 Zombies. I can connect but my friend can't connect to the same server, we are in the same Lan-Network. As Usally when me , my friend and my sister play , my sister have the same issue ( always Connect to server , or Joining game session ) or Downloading game details or smth, ) .

My friend cant join me , yesterday it works everything fine but now he cant even go on online ( connecting to server) infinite .