This is a bug in the iWeb component and to avoid this error, please run below script in SSMS and recycle application pool: UPDATE dbo.HostSettings SET SettingValue = 'false' WHERE SettingName = 'chkSpeedUp' GO This is to disable the speedup option for the email scheduler and this particular error is coming from that feature.
2017-04-11 10:24:06,032 [ETP02][Thread:113][ERROR] DotNetNuke.Services.Scheduling.Scheduler - Schedule Item Invalid: iWebs BulkEmailer EmailSchedule at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo) at System.Environment.get_StackTrace() at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.AddToScheduleQueue(ScheduleHistoryItem scheduleHistoryItem) at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.WorkCompleted(SchedulerClient schedulerClient) at DotNetNuke.Services.Scheduling.SchedulerClient.Completed() at DotNetNuke.Services.Scheduling.ProcessGroup.Run(ScheduleHistoryItem objScheduleHistoryItem) at DotNetNuke.Services.Scheduling.ProcessGroup.RunPooledThread(Object objScheduleHistoryItem) at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() at System.Threading.ThreadPoolWorkQueue.Dispatch() at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()