What operating system and browser? Would you be willing to test it in firefox for me to rule out a browser issue? You can download firefox here: http://www.mozilla.com
As I posted earlier, this is in Firefox 3.0.1 under Ubuntu Linux (for AMD64). I've run into the same issue in Konqueror, but I've not tested it as thoroughly there.
Ah sorry, missed that. I'm on firefox 3.0.1 Ubuntu AMD64 as well. Do you have any firefox plugins like "fasterfox" or cacheing utilities? Are you using a proxy or anything that could be affecting your cookies? I will PM you a test login to try that and see what happens.
I tried the account and password you sent via PM. It didn't log in. I've also tried disabling the proxy that I use to block nasties, but that didn't help. (The "click here if you're not redirected" page did start redirecting, but I still couldn't get in.)
Some additional information: I've just tried using another computer, running two OSs, with the same results. With both Firefox under Fedora Core 9 for x86 and Safari under MacOS X 10.5.2 I see the same behavior: The first login after launching the browser works, but subsequent logins fail.
Oh, and I don't have any unusual plugins installed.