Try each of the following steps until the issue is resolved. Back up all data before making any changes.
Step 1
Create a new calendar. Move the unwanted event(s) into it, then delete the new calendar.
Step 2
If the calendar server has a website, like iCloud or Google, log in to the website and delete the event.
Step 3
Quit Calendar. Triple-click anywhere in the line below on this page to select it:
~/Library/Calendars/Calendar Cache
Right-click or control-click the highlighted line and select
Services ▹ Reveal
from the contextual menu.* A Finder window should open with a file named "Calendar Cache" selected.
Move the selected file to the Trash. There may be one or two other files in the same folder with names that begin in "Calendar Cache". If so, delete those files too.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.
Step 4
Follow the instructions in this support article, then log out, log back in, and test.
Step 5
Start up in Recovery mode. When the OS X Utilities screen appears, select
Utilities ▹ Terminal
from the menu bar. A Terminal window will open.
In the Terminal window, type this:
resetp
Press the tab key. The partial command you typed will automatically be completed to this:
resetpassword
Press return. A Reset Password window will open. You’re not going to reset a password.
Select your startup volume ("Macintosh HD," unless you gave it a different name) if not already selected.
Select your username from the menu labeled
Select the user account
if not already selected.
Under
Reset Home Directory Permissions and ACLs
click the Reset button.
Select
▹ Restart
from the menu bar.
