Webmatrix only error with ajaxtoolkit

My application works correctly on the live production server, it runs windows 2008 and iis 7.

The same application throws the following exception on a dev server using webmatrix 3. This is a fresh install of windows 8 and webmatrix.

Value cannot be null.
Parameter name: httpBrowserCapabilities
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

 Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: httpBrowserCapabilities

Source Error:


 An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:



[ArgumentNullException: Value cannot be null.
Parameter name: httpBrowserCapabilities]
   System.Web.HttpBrowserCapabilitiesWrapper..ctor(HttpBrowserCapabilities httpBrowserCapabilities) +9502246
   System.Web.HttpRequestWrapper.get_Browser() +37
   System.Web.UI.PageRequestManager.OnInit() +61
   System.Web.UI.ScriptManager.OnInit(EventArgs e) +380
   AjaxControlToolkit.ToolkitScriptManager.OnInit(EventArgs e) +477
   System.Web.UI.Control.InitRecursive(Control namingContainer) +134
   System.Web.UI.Control.InitRecursive(Control namingContainer) +290
   System.Web.UI.Control.InitRecursive(Control namingContainer) +290
   System.Web.UI.Control.InitRecursive(Control namingContainer) +290
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +489

  


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.33440

The site is configured as follows in the applicationhost.config file:

<site name="TestSite" id="997005938"><application path="/" applicationPool="Clr4IntegratedAppPool"><virtualDirectory path="/" physicalPath="xxx" /></application><bindings><binding protocol="http" bindingInformation="*:37885:" /><binding protocol="https" bindingInformation="*:44301:" /></bindings><applicationDefaults applicationPool="Clr4IntegratedAppPool" /></site>