Resolution
To delete an enterprise calendar, complete the following steps:
1. Launch Microsoft Project Professional and log into Project Server with administrator permissions
2. Click Tools - Enterprise Options - Open Enterprise Global with Administrator
3. Click Tools - Organizer
4. Click the Calendars tab
5. Select the unneeded calendar from the list on the right (in the Enterprise Global)
6. Click the Delete button
7. Click the Close button
8. Save and close the Enterprise Global
9. Exit and relaunch Microsoft Project Professional