library learning L2

Server Error

Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
at events_presenter.Page_Load(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)