Ajax Tookit Editor error - MicrosoftAjax.debug.js Error Sys.ArgumentUndefinedException: Value cannot be undefined

Hi
I am using web developer 2010 express and Vista is the operating system. I downloaded Alaxtoolkit 4.00 ver and when I am using the editor  on my project and while running the
page the following error is coming from the page MicrosoftAjax.debug.js.. I tried many times but I cannot fix it  and could not find where is the problem . Other tool seems to be working fine.
 Microsoft JScript runtime error: Sys.ArgumentUndefinedException: Value cannot be undefined.
Parameter name: type
When I Break the code the following page  MicrosoftAjax.debug.js will appear
 // <param name="properties" optional="true" mayBeNull="true">A JSON object that describes the properties and their values.</param>
    /// <param name="events" optional="true" mayBeNull="true">A JSON object that describes the events and their handlers.</param>
    /// <param name="references" optional="true" mayBeNull="true">A JSON object that describes the properties that are references to other components.  The contents of this object consists of name/id pairs.  If in a two-pass creation, the setting of these properties will be delayed until the second pass.</param>
    /// <param name="element" domElement="true" optional="true" mayBeNull="true">The DOM element the component must be attached to.</param>
    /// <returns type="Object">The component instance.</returns>
    var e = Function._validateParams(arguments, [
        {name: "type", type: Type},
        {name: "properties", mayBeNull: true, optional: true},
        {name: "events", mayBeNull: true, optional: true},
        {name: "references", mayBeNull: true, optional: true},
        {name: "element", mayBeNull: true, domElement: true, optional: true}
    ]);
    if (e) throw e; //Error pointer is coming here     if (type.inheritsFrom(Sys.UI.Behavior) || type.inheritsFrom(Sys.UI.Control)) {
        if (!element) throw Error.argument('element', Sys.Res.createNoDom);
    }
    else if (element) throw Error.argument('element', Sys.Res.createComponentOnDom);
    var component = (element ? new type(element): new type());
    callIf(component, "beginUpdate");
    if (properties) {
        Sys.Component._setProperties(component, properties);