I have been struggling with some ASP AJAX code.  I moved the site from Server 2003 32-bit IIS6 to IIS7 on Server 2008 64-bit.  After a lot of searching and banging my head against the wall I found a blog on MSDN that told me how to add a binding redirect to my web config file so that the code would use the AJAX built into .NET 3.5.  Here it is. 


    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">


        <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35"/>

        <bindingRedirect oldVersion="" newVersion=""/>




Obtained from: