Private Sub DataGridView1_CellEndEdit(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellEndEdit

        DataGridView1.Rows(e.RowIndex).ErrorText = String.Empty

    End Sub

    Private Sub DataGridView1_CellValidating(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellValidatingEventArgs) Handles DataGridView1.CellValidating

        If DataGridView1.Columns(e.ColumnIndex).Name = "numero" Or DataGridView1.Columns(e.ColumnIndex).Name = "lunghezza" Then
            If Not IsNumeric(e.FormattedValue.ToString()) Then
                MsgBox("Volore non valido")
                'Oppure
                'DataGridView1.Rows(e.RowIndex).ErrorText = "Il valore non è numerico"
                e.Cancel = True
            End If
        End If

    End Sub