Workaround:   
  Sub New()
         
        InitializeComponent()
        AddHandler RadMessageBox.Instance.LocationChanged, AddressOf MsgLocationChanged
    End Sub
    Private Sub MsgLocationChanged(sender As Object, e As EventArgs)
        RadMessageBox.Instance.Location = New Point(Me.Location.X + Me.Width / 2 - RadMessageBox.Instance.Width / 2, _
                                                    Me.Location.Y + Me.Height / 2)
    End Sub