Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    FpSpread1.Dock = DockStyle.Fill
    Dim combo As FarPoint.Win.Spread.CellType.ComboBoxCellType = New FarPoint.Win.Spread.CellType.ComboBoxCellType()
    combo.Items = New String(2) {"a", "b", "c"}
    FpSpread1.ActiveSheet.Columns(0).CellType = combo
    AddHandler FpSpread1.Sheets(0).Models.Data.Changed, AddressOf Data_Changed
End Sub

Private Sub Data_Changed(ByVal sender As Object, ByVal e As FarPoint.Win.Spread.Model.SheetDataModelEventArgs)
    If TypeOf FpSpread1.ActiveSheet.Cells(e.Row, e.Column).CellType Is FarPoint.Win.Spread.CellType.ComboBoxCellType Then

        If FpSpread1.ActiveSheet.Cells(e.Row, e.Column).Value Is Nothing Then
            Console.WriteLine(e.Row.ToString() & ", " + e.Column.ToString())
        End If
    End If
End Sub