Backup your calendars.
Quit Calendar.
Then paste this text ~/Library into the Finder Menu > Go > Go to Folder… window and select “Go.”
This will open the Users Library Folder.
Open the Calendars Folder which is in that Library folder, and move any files with “Cache” listed in the name field to your Desktop.
Next, open the Preferences Folder in that same Library Folder and move the com.apple.iCal.plist file to the Desktop.
Log out/in or restart and open Calendar.
