title: Session "expires instantly" in IE after updating to ASP.NET 4? (FF works fine)
body: <p>I upgraded a .net 2.0 application to net 4.0 and now if I try to login with IE the session instantly expires. </p>
  
  <p>Does anyone have any ideas on where to look for this problem?</p>
  
  <p>Firefox works fine to log in.</p>
  
  <p>Thanks.</p>
  
  <p>Edit, More Information: Checking IE's cookies and firefox's cookies, it appears that a cookie is not being created in I.E, but it is being created in firefox.
  Any ideas on why this might be? Still digging into it but having a hard time...</p>
  
  <p>LAST EDIT; FIXED: Turns out this was not relevant to asp 4.0. I upgraded the application and set it up on a subdomain for testing to ensure everything worked, and the sub domain had an _ in it. After much research, IE will not take cookies from a domain with an _. This is done on purpose by design, apparently, since technically DNS rules forbid underscores in a domain. Changed to a - and it works.</p>