Recently while configuring a custom workflow on a document library I was getting the following message “The form cannot be displayed because session state is not available.”
And as a reason of the same I was not able to configure the workflow.
As the error message stated, the session state is not available. A quick look at the Site Collection web.config showed the following
As you can see in the above image, under httpModules the key “Session” with
type “System.Web.SessionState.SessionStateModule” was commented.
So after I uncommented the line and saved the file, the workflow worked like a charm.