Utilisation des Messages d'Erreur?

Private Sub CommandButton1_Click()
    ThisWorkbook.FollowHyperlink ActiveWorkbook.Path & "\" & "TARIF.xls"
    For i = 1 To Sheets.Count
        If Sheets(i).Cells(1, 4).Value = TABLIER Then
            Sheets(i).Activate
            Dim LARGEUR As Integer
            Dim HAUTEUR As Integer
            For Each L In ActiveSheet.Range(Cells(17, 2), Cells(17, 30))
                If L.Value = UserForm1.TextBox1.Text Then LARGEUR = L.Column
            Next
            For Each H In ActiveSheet.Range(Cells(18, 1), Cells(50, 1))
                If H.Value = UserForm1.TextBox2.Text Then HAUTEUR = H.Row
            Next
[COLOR=red]            If HAUTEUR = 0 Then[/COLOR]
[COLOR=red]                MsgBox ("Hauteur saisie incorrecte. Veuillez recommencer.")[/COLOR]
[COLOR=red]            ElseIf LARGEUR = 0 Then[/COLOR]
[COLOR=red]                MsgBox ("Largeur saisie incorrecte. Veuillez recommencer.")[/COLOR]
[COLOR=red]            Else[/COLOR]
[COLOR=red]                UserForm1.Label1.Caption = Round(ActiveSheet.Cells(HAUTEUR, LARGEUR).Value, 2)[/COLOR]
[COLOR=red]            End If[/COLOR]
        End If
    Next
    ActiveWorkbook.Save
    ActiveWorkbook.Close
End Sub