Hello ryeastman,
Thank you for using the Apple Support Communities!
It is my understanding you are experiencing an issue when trying to use Calendar on your MacBook Pro. Calendar is a great app that I rely on regularly. I will try my best to help you.
The first thing I would do is backup everything that is on the computer. Nothing I am going to suggest should cause any data loss, but it is always a good idea to have a backup. Your computer has software on it called Time Machine. It is fantastic software for backing up your computer. Information on how to use Time Machine is available here:
Use Time Machine to back up or restore your Mac.
Next, make sure that the MacBook Pro is running the latest OS X. To determine what OS X is currently installed, click on the Apple logo in the upper left corner and then click on About This Mac. The current version is El Capitan, Version 10.11.6. If needed, you can update using these instructions:
Update the software on your Mac
Get help using iCloud Contacts, Calendars, or Reminders, this article goes over some steps you'll want to check out, as well as, quitting the Calendar app and relaunching it while holding the shift key then test out adding an event.
If the OS X is up to date, and the issue is still present after following the above steps, it is important to try to isolate what is causing this to happen. The first thing to do to help isolate what is causing the problem is to start the computer in what is called safe mode and see if the problems still occur.
Starting up in safe mode
Follow these steps to start up into safe mode.
- Start or restart your Mac.
- Immediately after you hear the startup sound, press and hold the Shift key.
- Release the Shift key when you see the Apple logo appear on the screen.
After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.
Once the computer is running in safe mode, see if you can duplicate the issue. If Calendar works as expected, go ahead and try restarting normally again. If the issue is gone, it may have been caused by a cache file or directory issue that starting in safe mode fixed.
If the issue returns, you are going to want to check login items. You can find login items by clicking on the Apple Logo in the upper left corner, then click on System Preferences > Users & Groups.
Follow these instructions to remove the login items:
OS X El Capitan: If you think you have incompatible login items
Have a great day!