Same problem here. By the way my Outlook was on when I received this error... 2021-08-03 15:42:29 | Warning | Outlook exception, please assure that Outlook is running and not closed when syncing: You must specify a time. at Microsoft.Office.Interop.Outlook._AppointmentItem.get_Attachments() at GoContactSyncMod.AppointmentItemExtensions.ToDebugLog(AppointmentItem e, Boolean printRecurrenceExceptions) in .\AppointmentItemExtensions.cs:line 82 at GoContactSyncMod.Synchronizer.RemoveOutlookDuplicatedAppointments()...