I'm insert a dropdwon list in datagrid on row editing. wen i run the project the datasource is not rekognized>

<asp:TemplateField HeaderText="Lookup 1">
                            <EditItemTemplate>
                                   <asp:DropDownList    
                                   ID="Loocup1DropDownList"    
                                   Width="100%" 
                                   runat="server"  
                                   DataSource ="<%GetValueForDropDownCombinationContent()%>"
                                   DataValueField="LOOKUP_ID"
                                   DataTextField="lookup_name" >
                                </asp:DropDownList>

                            </EditItemTemplate>
                            <ItemTemplate>
                                <asp:Label ID="LOOKUP1_NAME" runat="server" Text='<%# Bind("LOOKUP1_NAME") %>'></asp:Label>
                            </ItemTemplate>

This is the vb.net function

Protected Function GetValueForDropDownCombinationContent() As IDataSource

    Dim dsProductLookups As New DataSet
    dsProductLookups = DocumentManager.Data.DataRepository.Provider.ExecuteDataSet("sp_GetCombinationsLookups", productCombo.SelectedValue)
    Return dsProductLookups
End Function

any ideas???