ez.no / exponential / documentation / faq / general / why can't i login to my sit...
This could happen if you use underscore, '_', in your host name. (For example, "my_host.com".) Internet Explorer will refuse to store any cookie information in this case, which makes login impossible. For more information see:
http://no2.php.net/manual/en/function.session-start.php#33369
http://www.zvon.org/tmRFC/RFC882/Output/chapter5.html