The error code is usually for server maintenance.
Check in with
www.CombatArms.Nexon.net to see what's going on, hopefully there's information up, if not, expect it up in a short time period.
You may receive different error codes though, so bear in mind, it may or may not be the server.
Don't always assume it's the server, my friend did it for 3 hours, then he looks down at his laptop, and finds he accidentally hit off the internet connection switch.
Make sure your firewall/antivirus/etc isn't blocking access to Combat Arms.
Hope your problem was fixed, and you're able to play now.
Thanks for posting.