Hi headrush1111,
1. How did the use send the sharing request, via Outlook Client or via Outlook Web App? Please let user try to share his calendar via Outlook Web App (http://mail.office365.com) and see if any updates.
2. I understand the issuing user can only share his calendar to some users. Given the situation, I would like to know if he can only share calendar to internal users (belong to the same domain), but cannot external users (belong to different domain).
3. It is appreciated you can provide screenshot here to help us understand the error message. You can post the screenshots here by clicking Use rich formatting, and clicking Insert Image icon.
Thanks,
Maggie Li