Enable SessionState Issue in ASP.NET and Sharepoint 2010

Question

I've been struggling for a week now, I can't find a solution for my problem. I'm fairly new to Sharepoint and want to create a simple webpart.

For this, I need a Session where I can store my DataTable, which contains data from a database.

E.g.:

private void storeDataTable(DataTable dt)
{
    Session["dtSession"] = dt;
}

When I'm debugging this code, an exception is thrown:

Session state can only be used when enableSessionState is set to true, either in a 
configuration file or in the Page directive. Please also make sure that      
System.Web.SessionStateModule or a custom session state module is included in the 
<configuration>\<system.web>\<httpModules> section in the application configuration

What I've done so far, to solve this issue:

1. Tried to enable SessionState in my ascx.cs - markup

   <%@ Control Language="C#" AutoEventWireup="true"  
   CodeBehind="MyWebPart.ascx.cs"      
   Inherits="MyWebPart.VisualWebPart.VisualWebPartUserControl" %>
   <%@ Page EnableSessionState="true" %>
   

   When I am running this, I got an exception:

   server tag is not well formed.
   

2. Add following to the web.config under "C:\inetpub\wwwroot\wss\VirtualDirectories\80\web.config"

   <pages enableSessionState="true" enableViewState="true" enableViewStateMac="true">
   

   and

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

   3.Run the following in the SharePoint 2010 Management Shell:

   Enable-SPSessionStateService –DefaultProvision
   

   4.Activate the ASP.NET State service under services.msc and change start to automatic.

None of this steps could resolve my issue.

Answer 1

I was able to solve my issue myself. I've searched through both of the web.configs (VirtualDirectories\80 and VirtualDirectories\7099) and deleted some entrys. Now I got the following entries in my web.config:

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

and

 <pages enableSessionState="true" enableViewState="true" enableViewStateMac="true" enableEventValidation="true" etc...>

I guess my fault was to have another SessionState declared which was costum. I've deleted these entries and the application works like a charm. So it seems, the exception will also be thrown, when there are to many Sessions declared.