执行命令定义时发生错误。有关mvc 4中的详细信息，请参阅内部异常

Question

我在下拉列表控件上收到以下错误：

An error occurred while executing the command definition. See the inner exception for details.

以下是崩溃的视图代码：

@Html.DropDownList("PackageId", null, htmlAttributes: new { @class = "form-control" })

这是控制器代码，我在其中获取下拉列表的数据：

ViewBag.PackageId = new SelectList(db.Packages, "u_package_id", "package_nme");

这是包控制器，以防需要：

public class Package
    {
        [Key]
        public int u_package_id { get; set; }

        public string package_type_cd { get; set; }

        public string package_nme { get; set; }

        public string status { get; set; }

        public string modify_user_id { get; set;}

        public DateTime modify_dt { get; set; }

        public string package_category { get; set; } 

        public string i_package_nme { get; set; }

        public Guid msrepl_tran_version { get; set; }

        public string InvoicePackageName { get; set; }

        public DateTime CreateDate { get; set; }

        public DateTime LastModifyDate { get; set; }

        public string invoice_package_nme { get; set; }

        public Boolean InSTCUSAFlag { get; set; }

        public string InSTCUSADisplayedName { get; set; }

        public string InSTCUSADisplayedDescription { get; set; }

        public Boolean PrerequisiteFlag { get; set; }

        public Guid PrerequisiteID  { get; set; }
    }
}