Random InvalidCastException

我在有自定义类的Dictionaries和Lists中得到了这个异常。示例：

 List<DisplayAllQuestionsTable> dsa = (List<DisplayAllQuestionsTable>)Session["Display"];

当我使用会话时，演员会工作10-20次。。然后它开始抛出异常。如果我在电脑上生活大约20-30分钟。。我可以像往常一样启动我的web应用程序，在启动代码20次后，它会抛出同样的异常。为什么会发生这种情况？

现在我用Sesson测试了另一个更简单的代码：

public partial class Default2 : System.Web.UI.Page
{
    List<meem> moom = new List<meem>();
    protected void Page_Load(object sender, EventArgs e)
    {

       for (int i = 0; i < 20; i++)
            {
                meem m = new meem();
                m.i = i;
                moom.Add(m);
            }

       Session["meem"] = moom;
        Button ew = new Button();
        ew.Text = "Press me";
        ew.Click += Click;
        PlaceHolder1.Controls.Add(ew);
    }
    void Click(object sender, EventArgs e)
    {
        List<meem> moom = (List<meem>)Session["meem"];
        foreach (var item in moom)
        {
            Label l = new Label();
            l.Text = item.i.ToString();
            this.Controls.Add(l);
        }
    }

}
class meem
{
    public int i;
}

它的工作原理是100%

我得到的例外：

    Server Error in '/WebSite10' Application.
[A]System.Collections.Generic.List`1[DisplayAllQuestionsTable] cannot be cast to 
[B]System.Collections.Generic.List`1[DisplayAllQuestionsTable]. 
Type A originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' 
    at location 'D:'WINDOWS'Microsoft.Net'assembly'GAC_32'mscorlib'v4.0_4.0.0.0__b77a5c561934e089'mscorlib.dll'. 
Type B originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' 
   at location          'D:'WINDOWS'Microsoft.Net'assembly'GAC_32'mscorlib'v4.0_4.0.0.0__b77a5c561934e089'mscorlib.dll'.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.InvalidCastException: [A]System.Collections.Generic.List`1[DisplayAllQuestionsTable] cannot be cast to [B]System.Collections.Generic.List`1[DisplayAllQuestionsTable]. Type A originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' at location 'D:'WINDOWS'Microsoft.Net'assembly'GAC_32'mscorlib'v4.0_4.0.0.0__b77a5c561934e089'mscorlib.dll'. Type B originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' at location 'D:'WINDOWS'Microsoft.Net'assembly'GAC_32'mscorlib'v4.0_4.0.0.0__b77a5c561934e089'mscorlib.dll'.