Q:

load balancing and loss of session state for user in ASP.NET web forms application

So I used a machine key generation web app to generate a machineKey element. I then put it in the web.config in its appropriate spot. The server admin deployed to both servers and pointed the load balancer at them.
For whatever reason, when I go to the preprod load balanced site, it works fine. I login, do the stuff on site, all is well in the world. However, there is a user that repeatedly goes to the site and has issues where the symptom is session state being lost. I looked at his message and it is basically login succeeds, stores items in session state, redirects to a page, checks the items which come back as null and then gives he message.
Why am I not experiencing this but he is? More importantly, how do I make sure he doesn't keep losing session state?

A:

Found what the issue was, but unfortunately based on the question not enough information was given to probably come to this:
1) This issue was only impacting Internet Explorer as far as can be figured out.
2) The hostname included an underscore in the name (server administrator given)

This is a case where Internet Explorer gets it right. The hostname included an underscore which makes it invalid. Internet Explorer refuses to create a cookie due to this fact (at least by default. Not sure if you can override the behavior within Internet Explorer). My guess is that Firefox and Chrome just turn the blind eye to it and work accordingly.
After requesting and receiving a rename for the URL, Internet Explorer was working again.

