Private Function checkDate(aCtrl As TextBox) As Date
        Dim aDate As Date
        While Date.TryParse(aCtrl.Text, aDate) = False
            If Date.TryParse(InputBox("Please re-enter date. Entry has to be a valid date", "Error"), aDate) = True Then
                aCtrl.Text = aDate
            Else
                aCtrl.Text = ""
            End If

        End While
        Return aDate
    End Function