Issue
In the MPM, it is possible to creat a new Calendar object, but it is not possible to change or add information, it is not possible to Save.
Environment
MPM
Cause
The User Rights does not allowed you to Save your changes in the Calendar objects.
Resolution
In the MPM, right click on the top right, where it says Management.
Select Permissions, and verify that the user that are logged in at the moment have permissions to Edit/View Calendar Objects.
