I have a Windows 2003 server with Visual Studio .NET installed.

I create a new web application (using c# and asp.net)

On the webform1.aspx I add a button from the toolbox, and in the
button1_click event simply add the code:

private void Button1_Click(object sender, System.EventArgs e)
{
Session["test"] = "123";
Response.Write(Session["test"]);
}

What should happen is that a button is displayed and when clicked the
text 123 is rendered to screen.

However, clicking the button gives error:

Session state can only be used when enableSessionState is set to true,
either in configuration file or in the page directive.

My web.config has section

     <sessionState 
            mode="InProc"
            stateConnectionString="tcpip=127.0.0.1:42424"
            sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
            cookieless="false" 
            timeout="20" 
    />

My question therefore is - why is session state not working - what do
I need to do to make it work?

I always took it for granted!!

look for 
<%@ ... Page EnableSessionState="false" ... %>
in webform1.aspx

First line of webform1.aspx is
<%@ Page language="c#" Codebehind="WebForm1.aspx.cs"
EnableSessionState="true" AutoEventWireup="false"
Inherits="GregBuczek.WebForm1" %>

Send files .cs .aspx

Where can I send them to?

Simon,
  Why don't you just open your web.config file and add the attribute
enableSessionState="true".  It would then look something like this:

     <sessionState 
            mode="InProc"
            enableSessionState="true"
            stateConnectionString="tcpip=127.0.0.1:42424"
            sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
            cookieless="false" 
            timeout="20" 
    />

Hope this helps,
                Nick Parker

Thanks for the reply... 

Modified the web config as suggested, although still getting same error:

'session state can only be used when enableSessionState is set to true
either in a configuration file or in the page directive'

(... which it obviously is!!)

And, indeed, even doing Response.Write(Session.SessionID.ToString());
gives same error.  So it is definately unhappy with session state :(

Any more ideas would be appreciated!

By default it takes inproc. If u change inproc to stateserver do the
following process. start -- control panel -- administrative tool -->
services -- select asp.net state server  by default it is stopped.
start this. and try your application.