Problem in calling Linq method which return group by result on page load

Thanks a lot dear..But My method is defined in class file and there Grid view is not detecting...I m making a windows application.
It is showing error like this:
Error 1 The type or namespace name 'GridView' could not be found (are you missing a using directive or an assembly reference?) D:\Work\testlinq\testlinq\DataClasses1.cs 381 43 testlinq

can u help me in this...

http://www.c-sharpcorner.com/UploadFile/VIMAL.LAKHERA/LINQResultsetToDatatable06242008042629AM/LINQResultsetToDatatable.aspx
 
Hope this link will help you convert the return type,.

May not be the best solution but it works

public static void GetPaymentGroupBy(GridView gv)
{
DataClasses1DataContext obj = new DataClasses1DataContext();
var query = (from pay in obj.GetTable<Payplan_Installment>()
group pay.Frequency by
new
{
pay.InstallmentAmount,
pay.PaymentMode,
pay.PlanStatus
} into details
select details);

gv.DataSource = query;
gv.DataBind();
}

DataClasses1DataContext.GetPaymentGroupBy(dataGridView1);