In one class, after having converted that to VS 2005, I see that the compiler shows some unknown references in the code under FlatStyle.System. What should I do to resolve that?

Imports System.Windows.Forms
Imports System.Drawing

<ToolboxBitmap(GetType(Label))> _
Public Class LXLabel
    Inherits System.Windows.Forms.Label

    Public Sub New()
        Me.FlatStyle = FlatStyle.System
    End Sub

End Class