http://blogs.msdn.com/tom/archive/2008/07/14/unable-to-use-session-state-server.aspxIssue ASP.NET site running under .NET 2.0 has the following setting in web.config: &lt;sessionState mode=&quot;StateServer&quot; stateNetworkTimeout=&quot;10&quot; cookieless=&quot;false&quot; timeout=&quot;30&quot;/&gt; When the application attemptsen-USCommunityServer 2.1 SP1 (Build: 61025.2)http://blogs.msdn.com/tom/archive/2008/07/14/unable-to-use-session-state-server.aspx#8731278Mon, 14 Jul 2008 13:19:08 GMT91d46819-8472-40ad-a661-2c78acb4018c:8731278a-foton &raquo; Unable to use Session State Server<p>PingBack from <a rel="nofollow" target="_new" href="http://blog.a-foton.ru/2008/07/unable-to-use-session-state-server/">http://blog.a-foton.ru/2008/07/unable-to-use-session-state-server/</a></p> http://blogs.msdn.com/tom/archive/2008/07/14/unable-to-use-session-state-server.aspx#9809780Tue, 30 Jun 2009 19:19:37 GMT91d46819-8472-40ad-a661-2c78acb4018c:9809780Boris<p>Good article, however didn't solve the issue. I've set enableVersionHeader &nbsp;to &quot;true&quot; and confirmed with fiddler that response contains version headers, but still seeing the issue</p>http://blogs.msdn.com/tom/archive/2008/07/14/unable-to-use-session-state-server.aspx#9891915Sun, 06 Sep 2009 13:44:41 GMT91d46819-8472-40ad-a661-2c78acb4018c:9891915Mick Byrne<p>This is a really nice clear article, but does not explain how to solve the problem. I would love to get an answer as to how to prevent this from happening...</p>http://blogs.msdn.com/tom/archive/2008/07/14/unable-to-use-session-state-server.aspx#9892267Mon, 07 Sep 2009 19:09:47 GMT91d46819-8472-40ad-a661-2c78acb4018c:9892267Tom<p>The solution given here is to look at the HTTP headers and see if X-ASPNet-Version is there. &nbsp;If not, check that setting. &nbsp;As that header missing will cause the problem.</p>