Avast firewall is blocking my Runescape!

Hey guys! So Im having this problem, where when I try to turn my Runescape client on it just stays at 0% and gives me "There was an error loading the game configuration from the website. If you have a firewall, check that this program is allowed to access the internet" I checked my windows firewall and error was still there. Only when I disabled my avast firewall I could play the game. This is where I need help. Can someone tell me how to let runescape get trough avast firewall? Thanks in advance.