I am having a similar problem with trying to attach to a calendar within my primary Outlook account. The calendar is name Staff Absences but when I try to attach to it, I get the same error.
Set myCalItems = olNS.GetSharedDefaultFolder(objRecipient, 9).Items '9=olFolderCalendar
Is it possible to attach to a subcalendar (or created one). I have shared the calendar but it will not attach to it with your app.
I love your app.