Error 403 when saving meeting to Google Calendar

Hi.  I'm a PRO user. Every time I create a new meeting and try to save it, with instructions to post the meeting to my Google Calendar, I get this error:

403 Forbidden POST https://www.googleapis.com/calendar/v3/calendars/primary/events { "code" : 403, "errors" : [ { "domain" : "global", "message" : "Insufficient Permission", "reason" : "insufficientPermissions" } ], "message" : "Request had insufficient authentication scopes.", "status" : "PERMISSION_DENIED" } (-1)

I've gone through the calendar settings but still coming up empty.  Any help appreciated.