Требовать проверку поля в Telerik GridDropDownColumn

Я занимаюсь этим довольно давно, и у меня это действительно хорошо сработало.

<telerik:GridTemplateColumn HeaderText = "Depatment Type" UniqueName = "DEPT_ID">
    <ItemTemplate>
        <asp:Label runat = "server" ID = "lblDeptName"
    </ItemTemplate>
    <EditItemTemplate>
        <telerik:RadDropDownList runat = "server" ID = "comboDepts"
            DataSourceID = "SqlDSDeptType"
            DataTextField = "DEPT_NAME" DataValueField = "DEPT_ID">
        </telerik:RadDropDownList>
        <asp:RequiredFieldValidator ID = "rfvcomboDepts" runat = "server"
            Display = "Dynamic" CssClass = "validationClass"
            ValidationGroup = "grvgName"
            ControlToValidate = "comboDepts"
            ErrorMessage = "Department cannot be empty"></asp:RequiredFieldValidator>
    </EditItemTemplate>
    <InsertItemTemplate>
        <telerik:RadDropDownList runat = "server" ID = "comboDepts"
            DataSourceID = "SqlDSDeptType"
            DataTextField = "DEPT_NAME" DataValueField = "DEPT_ID">
        </telerik:RadDropDownList>
        <asp:RequiredFieldValidator ID = "rfvcomboDepts" runat = "server"
            Display = "Dynamic" CssClass = "validationClass"
            ValidationGroup = "grvgName"
            ControlToValidate = "comboDepts"
            ErrorMessage = "Department cannot be empty"></asp:RequiredFieldValidator>
    </InsertItemTemplate>
</telerik:GridTemplateColumn>

CSS

.validationClass {
    background-color: #FFCCCC;
    color: black;
    font-weight: bold;
}