以下をフォームのコードに追加
' CreateParams プロパティをオーバーライドする
Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
Get
Const CS_NOCLOSE As Integer = &H200
Dim DcreateParams As System.Windows.Forms.CreateParams = MyBase.CreateParams
DcreateParams .ClassStyle = DcreateParams .ClassStyle Or CS_NOCLOSE
Return DcreateParams
End Get
End Property