c#.net无效强制转换异常

c#.net无效强制转换异常：

[A] GroupReference不能强制转换为[B]GroupReference。A类源自"App_Code.d7jdf1ji，版本=0.0.0.0，区域性=中性，位置处上下文"Default"中的PublicKeyToken=null'C:''Windows''Microsoft。NET''Framework''v4.0.30119''临时ASP。NETFiles''root''26676eb7''92c7e946''App_Code.d7jdf1ji.dll。类型B源自来自"App_Code.t8v3riip，版本=0.0.0.0，区域性=中性，位置处上下文"Default"中的PublicKeyToken=null'C:''Windows''Microsoft。NET''Framework''v4.0.30119''临时ASP。NETFiles''root''26676eb7''92c7e946''App_Code.t8v3riip.dll’

这是我的代码

public partial class packages : System.Web.UI.Page
{
    GroupReference gr_object;
    DataConnect dc_object;

    protected void Page_Load(object sender, EventArgs e)
    {
        gr_object = (GroupReference)Session["GroupReference"];
        dc_object = (DataConnect)Session["DataConnect"];
    if (!IsPostBack)
    {
        Page.EnableViewState = false;
        Welcome.Text = "packages end date is the day it is requested.<br/><br/>";
        Data.init();
        HideControls();
        packages();
        packagess_Grid_Active.Visible = true;
        packages_Grid_Inactive.Visible = true;
        SaveAsExcelButton_Active.Visible = true;
        SaveAsExcelButton_Inactive.Visible = true;
        ShowControls();
        Usage.RecordUse("packages");
    }
}
protected void packages()
{
    OracleConnection oc = dc_object.oc_object.Connect();
    OracleCommand ocmd = new OracleCommand();
    OracleDataReader dr;
    ocmd.Connection = oc;
    ocmd.CommandText = "SELECT * from packages"; 
    ocmd.CommandType = CommandType.Text;
    dr = ocmd.ExecuteReader();