Today, I encountered an interesting issue with SharePoint calendar list items. My customer had created a recurring calendar entry using Outlook and then subsequently deleted the series in Outlook. Somewhere along the timeline they may have updated specific instances in the series. After deleting the series my customer noticed future events in the recurrence series remaining in the SharePoint Calendar list. Any attempt to delete these list items via the UI or PowerShell resulted in the error “Item Does Not exist. It may have been deleted by another user“.
SharePoint handles recurring events by creating child list items for every event in the series and tying them to one master list item – stored in the MasterSeriesItemID field. The master list item is not shown via the UI, since users see the events in the series, especially when the series has exceptions.
Deleting the master list item with ID specified in MasterSeriesItemID resulted in deleting the entire set of recurring events in the series, which was the desired outcome. I’m guessing Outlook should have deleted the series master item in SharePoint when the user deleted the series in Outlook, but that clearly didn’t happen.