I'm working on an exercise straight from an ASP.NET book. It has to do 
with creating pages that can run on mobile devices. It worked fine until I 
added the attribute Decoration="Numbered" in the Mobile:List element. Now 
it produces the following message:

Unable to make the session state request to the session state server. Make 
sure that the ASP.NET State service is started and that the client and 
server ports are the same.

The same code without the Decoration attribute continues to work fine.

Here is the code that produces the error:

<%@ Page Inherits="System.Web.UI.MobileControls.MobilePage" %>
<%@ Register TagPrefix="Mobile" Namespace="System.Web.UI.MobileControls" 
Assembly="System.Web.Mobile" %>

<Mobile:Form runat="server">
<b>Now Playing:</b>
<br/>
<Mobile:List Decoration="Numbered" runat="server">
  <Item Text="Star Wars" />
  <Item Text="Gone with the Wind" />
  <Item Text="Citizen Kane" />
</Mobile:List>
</Mobile:Form>