I have successfully upgraded Sitecore 8.0 rev. 150812 to Sitecore 8.1. But when I deployed my project, it stopped work. I have found following error message in Windows event viewer: "Could not load type 'Sitecore.SessionManagement.ConditionalSessionIdManager. (C:...\Website\web.config line 191)"
That's session state node from web.config file:
"sessionState mode="InProc" cookieless="false" timeout="20" sessionIDManagerType="Sitecore.SessionManagement.ConditionalSessionIdManager""
I have noted this node was changed due Sitecore upgrading. The previous version is:
"sessionState mode="InProc" cookieless="false" timeout="20" sessionIDManagerType="Sitecore.FXM.SessionManagement.ConditionalSessionIdManager""
(FXM is added)
It looks like my deployment have changed some important dll, but I don't know which one.
In Sitecore 8.1 ConditionalSessionIdManager is in Sitecore.Kernal.dll.
And it used to be in Sitecore.FXM.dll in Sitecore 8.0.
What is the version of Sitecore.Kernel.dll in the environment to which you did the deploy?
Does is say Product version: 8.1.0 rev...?
It looks like your deployment process copied Sitecore.Kernel.dll (and possibly some other Sitecore libraries) from the old Sitecore version.