Laufzeitfehler

Private Sub ComboBox2_Change()
Dim i_l As Integer
Dim i As Integer
Dim ws As Worksheet
Dim a As Variant
Set ws = Worksheets("Tabelle")
i = Selection.Row
a = ComboBox2.Value
Do While ws.Cells(i, 2)  a
i = i + 1
Loop
ws.Cells(i, 2).Select
End Sub