Why cant I log on sometime ?

ok so sometime i dont know why but when I try to log on it says whitelisted server and I keep refreshing and it stills says that. Luckily that only happens sometimes but i still get a bit frustrated because
of that. I also noticed that it happens when it says virody build server(something like that). What can I do to prevent these situations and how do I make it so i can log on anytime ?