PRB: Session variables are lost intermittently in ASP.NET applications

Steps to reproduce the behavior

1. Follow these steps to create a Web application in Microsoft Visual Basic .NET:
   1. Open Microsoft Visual Studio .NET.
   2. On the File menu, point to New, and then click Project.
   3. In the New Project dialog box, click Visual Basic Projects under Project Types, and then click ASP.NET Web Application under Templates.
   4. In the Location text box, type http://localhost/TestWeb1.
   5. Click OK to create the project. WebForm1.aspx is added to your project by default.
2. In the Solution Explorer window, right-click WebForm1.aspx, and then click View Code.
3. Add the following code to the Page_Load event procedure:

   Response.Write("<b>Session Variable Test</b><br>&#xa0;<br>")
   If IsNothing(Session("TestVal")) Then
       Response.Write("TestVal old value: <b>nothing</b>")
       Session("TestVal") = 0
   Else
       Response.Write("TestVal old value: " & Session("TestVal"))
   End If
   Session("TestVal") += 1
   Response.Write("<br>TestVal new value: " & Session("TestVal"))
   

4. On the Build menu, click Build Solution.
5. In the Solution Explorer window, right-click WebForm1.aspx, and then click View in Browser.
6. In your browser, click Refresh. Notice that the page displays the initial value of the session variable as nothing.
7. Click Refresh again several times. Notice that the initial value of the session variable changes to a number that increments whenever you refresh the page.
8. Leave the page open in your browser.
9. In Notepad, open the Global.asax file from your project's folder. The Global.asax file of this TestWeb1 project is typically located in the C:\Inetpub\wwwroot\TestWeb1\Global.asax folder.
10. Move the insertion point to a blank line in the Global.asax file, and then press ENTER to add a second blank line. You must perform this step to mark the file as having been modified.
11. Save your changes to the Global.asax file.
12. In the browser, click Refresh again. Notice that the TestVal session variable displays an initial value of nothing. Your in-process session variables are lost.