If you are wondering why you can't join at the moment, Mojang's authentication servers are currently down for maintenance. Until they come back up, getting in-game will be difficult, and there is nothing we can do on our end to help.
You may visit this thread throughout the period of the authentication servers being down to receive updates on it's status.
~ MCRPG Staff Team
Update 1: Servers have gone back up, and everything should be ok. Enjoy!