How to Enable Session State in SharePoint 2010 ?

To enable Session State you will first need to add the SessionStateModule to the  web.config file as shown below:

< httpModules >
< add name = "Session " type = "System.Web.SessionState.SessionStateModule " />
</ httpModules >

Next you need to edit your web application in the IIS Management Console and add the same session state module to the IIS7 managed pipeline.

1. Open the IIS 7 Management Console, and navigate to  your web application.
2. Double click “Modules” in the IIS section.
3. Click “Add Managed Module…” on the right panel.
4. In the Add Managed Module dialog, enter a name such as “SessionState”  and then choose the below  item from the dropdown:
   System.Web.SessionState.SessionStateModule, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

That’s it! Session State should then work in your SharePoint app