IE7 and IE8 cannot support URI’s with underscores
Stumbled upon this. If you’re going to make a URI (domain or sub domain) with an underscore, think twice. IE7 and IE8 do not support these URI’s when dealing with cookies.
For more details, see this blog post, detailing the symptoms.
http://blog.patrick-morgan.net/2008/09/problems-with-ie7-sessions-not-saved-in.html

