ExecuteByIdUserQuery with Silverlight

Hello,

in my Silverlight application for CRM 2011, I want to get the results of the saved query. I have this code for it:

private void Begin()
{
    OrganizationRequest request = new OrganizationRequest()
    {
        RequestName = "ExecuteByIdUserQuery"
    };
    request["EntityId"] = new Guid("b580c970-bf52-e211-8aa3-984be17c9a93");
    request["EntityFilters"] = EntityFilters.Entity;
    request["LogicalName"] = "userquery";
    request["MetadataId"] = Guid.Empty;
    request["RetrieveAsIfPublished"] = false;
}

private void End(IAsyncResult ar)
{
    OrganizationResponse resp = service.EndExecute(ar);
}

The problem is, it goes to the End method and fails on the EndExecute with CommunicationException and message: The remote server returned an error: Not found.

I am sure, that the guid I use exists. When I use this type of code with other requests, like RetrieveEntity, it works fine. Only this ExecuteByIdUserQuery doesn't.

Thanks for your answers.

Tom