Since recently my calendar shows (2) behind it in blue. Did I somehow copy my calendar? I cannot rename it back either.
The number in blue behind the Calendar folder indicates the amount of unread items in it.
Usually you get an unread item notification when you import a vcs or ical file you got sent as an email attachment or downloaded from a website.
If you don’t care about which items these are, then you can simply right click on the Calendar folder and choose “Mark All as Read”.
If you do want to find out which items these are, then you can best change your view to All Appointments;
All Outlook versions except Outlook 2003: View-> Current View-> All Appointments
Outlook 2003: View-> Arrange By-> Current View-> All Appointments
The unread items will show in bold.
If you still can’t find them then, then you can filter the All Appointments list to show the Unread Items only;
View-> Arrange By-> Custom-> Filter…-> tab More Choices-> select: Only items that are unread