Yorick, what if you try logging in using 127.0.0.1 instead of localhost?
Makes no difference. I seem to be abe to access the control panel’s homepage by hacking around in Core.php but I get a non authorized error on any other page (along with erros on the homepage).
My guess is that it somehow fails to store the session on the browser. I tried Safari and Firefox but none of them worked, so it’s not a browser specific issue.