Hi headrush1111,
As I understand it, one of your users is not able to share his calendar to certain person. Firstly, would you like to ensure the proper configuration by referring to this online instruction? Sharing a Calendar
If the issue persists, I will appreciate it if you provide the following information for further troubleshooting.
1. Is the user available to share his calendar to other persons?
2. Could the certain person add other users’ calendars?
3. When did he get the error message “policy error”? For example, sending sharing request, adding shared calendar. In addition, it will be nice if you can post the screenshot with the detailed error message.
Thanks,
Maggie Li