Restart blockland and make sure your internet connection is good.
Are you by any chance using any Proxy or VPN?^ this too
What have you changed on your computer lately? Have you installed anything new, like Hamachi?
If you go to the options menu and then look in the advanced tab, there should be something called "Disable Vertex Buffer Objects." Toggle it and see what happens.
Please use this tool to determine if you are behind a proxy.http://www.lagado.com/proxy-test
Are you still having this error? I would check to see if anyone you know has your key.
Yes, also, I have a laptop and a PC with the keys.