how to bind the data to grid view using silverlight and wcf service

i don't have permission to access Google and i know how to bind the data to data grid using data reader in silverlight using wcf service but when i'm trying to use dataadapter i got the error that why i posted my question

k this ismy MainPage.xaml code
namespace SilverLightGridView
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
Service1Client Client = new Service1Client();
Client.GetQualificationCompleted += new EventHandler<getqualificationcompletedeventargs>(Client_GetQualificationCompleted);
Client.GetQualificationAsync();
}

void Client_GetQualificationCompleted(object sender, GetQualificationCompletedEventArgs e)
{
GridviewQualification.ItemsSource = e.Result;
}


}
}
and this is my Wcf Service
namespace SilverLightGridView.Web
{
[ServiceContract(Namespace = "")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class Service1
{
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ToString());
[OperationContract]
public DataSet GetQualification()
{
SqlDataAdapter da = new SqlDataAdapter("Web_Svt_SelectQualification", con);
DataSet ds = new DataSet();
da.Fill(ds);
return ds;
}
}
}
i got the error near "e.result";
Error is :Cannot implicitly convert type 'SilverLightGridView.ServiceReference1.ArrayOfXElement' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?)