1. Your browser - I know that there's been some issues with the whole IRC Live Chat thing before, it might just be your browser. Which do you use?
2. Firewall or Security Measures - I know that this has been an issue for me recently. After I've logged in, the following security warning appears:
Now, the issue that arises from this is accidentally pressing "Yes" when you're acting careless and quickly. This was happening to me, and I was about to post in the Question Centre much like you did before I finally figured it out. This is what shows up after clicking "Yes". Although, it would appear your problem is different. Still, this could be used as a guide in the future.
Like I said, your error code is different. This may or may not be your problem, but clearly your problem is security in some way, shape or form. So, just make sure you click "No", not "Yes".
Hope this helped! If not, Google it or something. I'm sure it's happened a lot before.