Ошибка шага «Активировать функцию»: ссылка на объект не указывает на экземпляр объекта

Я создал собственное задание таймера и реализовал его через событие функции в sharepoint.

когда я пытался активировать его, он показывает эту конкретную ошибку:

Object reference not set to an instance of an object.   at TimerJobExample.MyFeatureReceiver.FeatureActivated(SPFeatureReceiverProperties properties) in C:\Documents and Settings\admin-shuklag.INFRADEV\My Documents\Visual Studio 2008\Projects\TimerJobExample\TimerJobExample\MyFeatureReceiver.cs:line 22 
   at Microsoft.SharePoint.SPFeature.DoActivationCallout(Boolean fActivate, Boolean fForce) 
   at Microsoft.SharePoint.SPFeature.Activate(SPSite siteParent, SPWeb webParent, SPFeaturePropertyCollection props, Boolean fForce) 
   at Microsoft.SharePoint.SPFeatureCollection.AddInternal(Guid featureId, SPFeaturePropertyCollection properties, Boolean force, Boolean fMarkOnly) 
   at Microsoft.SharePoint.SPFeatureCollection.Add(Guid featureId) 
   at Microsoft.SharePoint.WebControls.FeatureActivator.BtnActivateFeature_Click(Object objSender, EventArgs evtargs) 
   at System.Web.UI.WebControls.Button.OnClick(EventArgs e) 
   at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) 
   at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) 
   at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) 
   at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) 
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) 

Строка ошибки выделена ниже

public override void FeatureActivated(SPFeatureReceiverProperties properties)
    {

        SPSite site = properties.Feature.Parent as SPSite;

        // make sure the job isn't already registered


//error line
      **foreach (SPJobDefinition job in site.WebApplication.JobDefinitions)**

        {

            if (job.Name == List_JOB_NAME)

                job.Delete();

        }



        SampleTimer listLoggerJob = new SampleTimer(List_JOB_NAME, site.WebApplication);

        SPMinuteSchedule schedule = new SPMinuteSchedule();

        schedule.BeginSecond = 0;

        schedule.EndSecond = 59;

        schedule.Interval = 5;

        listLoggerJob.Schedule = schedule;

        listLoggerJob.Update();

    }

В чем может быть проблема?