【トラブル】【ASP.NET】例外『Type XXX in Assembly 'YYYY' is not marked as serializable』が表示される

■ 概要

 * 以下「サンプル」のLinkButton1_Clickイベント処理後、
   例外『Type XXX in Assembly 'YYYY' is not marked as serializable』が表示される

■ サンプル

WebForm1.aspx

Protected Sub LinkButton1_Click(sender As Object, e As EventArgs) Handles LinkButton1.Click

    Dim oldModel As CompanyModel = New CompanyModel()
    oldModel.code = Me.TextBox1.Text
    oldModel.name = Me.TextBox2.Text

    ViewState("OldModel") = oldModel

    Me.MultiView1.SetActiveView(Me.View2)

End Sub

CompanyModel.vs

Public Class CompanyModel

#Region "Publicクラス変数"
    ''' <summary>
    ''' 会社コード
    ''' </summary>
    Public code As String

    ''' <summary>
    ''' 会社名
    ''' </summary>
    Public name As String
#End Region
End Class

■ 解決策

 * クラスの頭に、『<Serializable()>』を付ける

修正例

<Serializable()> _
Public Class CompanyModel
 ...