If the message given is "disconnected from ironclad online" but you're on 1.33, the problem is with the connection somewhere, not with anything else. The serial isn't the problem.
Like others said, try disabling any firewalls you have. Also exit Peerblock (or similar programs) if you have it, along with any other programs that use a lot of bandwidth (torrent clients, program updates, Steam...) That should clear your connection enough to connect to Ironclad.
That said, I've been having serious connectivity issues with ICO as well very recently, most likely due to the 1.33 update that was just released: I've been getting intermittent lag spikes of 20,000 or so, freezing the entire game for a time, before getting back to normal. The same thing's been evident in the lobby: when I log in, it often takes like 10 seconds for ICO to successfully display that I'm in the lobby... and it can take a similar long amount of time when I change an game setting option, like race or team.
This doesn't always happen - sometimes it responds pretty normally, at least for a short period of time - but this hasn't happened to me before, and started happening just as the 1.33 update was applied.
In short: the problem might be with ICO, and not with something on your end.
