Both domains map to 80.168.77.164 for me. This is a simple DNS propagation issue - some DNS servers have the new IP, others still have the old IP. The answer is to wait up to 48 hours for the new data to propagate to all DNS servers.
Oh, nevermind what I just said then. If you're both using the same ISP then either a router or a computer between you and your ISP is incorrectly resolving that domain. Are you sure you didn't add a HOSTS entry on your computer, Grey? Maybe while you were initially developing your site and waiting for the domain name to propagate? If that isn't it, try resetting your machine and any routers you have.
Call them and ask.
Grey uses the same ISP as me so I can't see this being the problem.
Oh, nevermind what I just said then. If you're both using the same ISP then either a router or a computer between you and your ISP is incorrectly resolving that domain. Are you sure you didn't add a HOSTS entry on your computer, Grey? Maybe while you were initially developing your site and waiting for the domain name to propagate? If that isn't it, try resetting your machine and any routers you have.
how can I find out if I'm behind an ISP proxy cache? And what to do about it?
Call them and ask.