textbox qui ne se remplie pas

Private Sub ComboBox3_Change()
With Sheets("Tableau")
    derligne = .Range("F" & Rows.Count).End(xlUp).Row
    For I = 5 To derligne
        If ComboBox3.Value <> "" Then
        TextBox1.Value = ""
        On Error GoTo fin
            If .Range("F" & I) = CSng(ComboBox3.Value) Then
                TextBox1 = .Range("G" & I)
                I = derligne
                End If
Else
     TextBox1.Value = ""
          End If
    Next I
End With
fin:
End Sub