I have some answers for this too:
1. This is a common user's mailbox.
2. Yes
3. No. I had no Outlook errors before accepting this shared calendar.
4. I don't have another shared calendar at this point.
Besides getting a million of these "Can't show the recurring calendar event" errors, I also get this one "Permission Error. Changes to the event "" could not be saved because you do not have the appropriate permission."