Binding combox in gridview with selected value of another comboBox

Hi all, I hope I got the right forum...

I can do what the subject states when the comboBox or DropDown is NOT in a gridview, as in the code below which populates the room DDL with the value that was selected in the building DDL

Protected Sub DDLbuilding_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DDLbuilding.SelectedIndexChanged
        'Create DataTable
        Dim dtRooms As New DataTable() ' - Room Numbers
        dtRooms.Columns.Add("Room", Type.GetType("System.String"))

        'Get Buildings for this campus
        RoomTable = RoomAdapter.GetRooms(DDLbuilding.SelectedValue)

        'Fill DataTable
        For Each RoomRow In RoomTable
            dtRooms.Rows.Add()
            dtRooms.Rows(dtRooms.Rows.Count - 1)("Room") = RoomRow.Room
        Next

        'bind DDLroom to datatable
        DDLroom.DataSource = dtRooms
        DDLroom.DataBind()
    End Sub

but when the comboBox or DDL is in a gridview it throws the error "Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control".

Here's what I have so far for the gridview comboBox

Protected Sub cbEQName_SelectedIndexChanged(sender As Object, e As EventArgs)

     'Get row index of selected comboBox
     Dim gvRow As GridViewRow = CType(CType(sender, Control).Parent.Parent, GridViewRow)
     Dim index As Integer = gvRow.RowIndex

     'Get selected value of selected comboBox
     EQname = TryCast(GVnewEquipment.Rows(index).FindControl("cbEQname"), AjaxControlToolkit.ComboBox).Text

     'Get new values of next comboBox from selected value of selected comboBox
     EquipmentTable = EquipmentAdapter.GetMfg(EQname)

     'Create DataTable
     Dim dtMfgs As New DataTable() ' - mfgs that are used by Equiptment name
     dtMfgs.Columns.Add("mfg", Type.GetType("System.String"))

     'Fill DataTable
     For Each EquipmentRow In EquipmentTable
         dtMfgs.Rows.Add()
         dtMfgs.Rows(dtMfgs.Rows.Count - 1)("mfg") = EquipmentRow.mfg
     Next

     'create ComboBox which will represent GVnewQuipment cbMfg comboBox
     Dim CB = DirectCast(GVnewEquipment.Rows(index).FindControl("cbMfg"), AjaxControlToolkit.ComboBox)

     'bind cbMfg to datatable
     CB.DataSource = dtMfgs
     CB.DataBind()

 End Sub

Any and help is greatly appreciated!!