How To: Activate ASP.NET Session (HttpContext.Current.Session is null)

Follow this steps to activate the ASP.NET Session in your Server:
1. Open the SharePoint Management Shell.
2. Execute the following command:

Enable-SPSessionStateService –DefaultProvision

3. You’ve to change the parameter “enableSessionState” to true on each web application you have:

pages enableSessionState="true" enableViewState=.....