EDIT: Go place a ticket at Nexon about it. You could try re-installing CA to feel like your doing something productive. Really, you can't connect to the server, and this message usually pops up when their servers are down. It might be your firewall settings, as in your firewall is preventing CA to connect to the internet. Check out what could be doing this on your end, but I suggest posting the problem with Nexon ASAP, cause it takes them a LONG time to answer it, assuming their answer helps you.
EDITEDIT: Oh yeah, alot of people will post that you "might be banned". I don't know if this is true, even though I read it alot. It could be true, and Nexon could be blocking your IP address, and not allowing your PC to connect with their servers. I think some people just post this shit to seem like they know what the fuck they're doing. Save the bullshit for your workplace, where it really matters. Anyone hiring???