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Error with Ajax-Enabled WCF Service (JSON) when consuming from jquery .ajax()
[ServiceContract(Namespace = "http://localhost/")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class Items
{
    [OperationContract]
    [WebGet]
    public string HelloWorld()
    {
        return "Hello World.";
    }
}

<services>
  <service name="OService.ReadServices.Items">
    <endpoint address="soap" binding="basicHttpBinding" contract="OService.ReadServices.Items"/>
    <endpoint address="json" binding="webHttpBinding"  behaviorConfiguration="jsonBehavior" contract="OService.ReadServices.Items"/>
  </service>
</services>

<endpointBehaviors>
    <behavior name="jsonBehavior">
      <enableWebScript />
    </behavior>
  </endpointBehaviors>

$(document).ready(function () {
    $.ajax({
        type: "POST",
        contentType: "application/json; charset=utf-8",
        url: "http://localhost/OService/ReadServices/Items.svc/json/HelloWorld",
        data: "{}",
        dataType: "json",
        success: function (msg) {
            alert("success: " + msg.d);
        },
        error: function (xhr, textStatus, errorThrown) {
            alert("error: " + textStatus + " - " + errorThrown + " - " + xhr);
        }
    });
});