Hi, cmarthur.
Thank you for visiting Apple Support Communities.
Try removing the preference to sync calendar events in iCloud preferences. Once this is down enable the preference again and see if this resolves the issue.
- Turn iCloud Calendars off and back on:
- Quit Calendar (or iCal).
- Choose
Apple () menu > System Preferences, then select iCloud.
- Deselect the checkbox next to Calendars.
- Close System Preferences and wait about a minute.
- Open System Preferences and select iCloud.
- Replace the checkmark next to Calendars.
- Close System Preferences.
- Open Calendar (or iCal) and test to see if the issue is resolved.
- Restart your computer. This may sound simple, but it reinitializes your network and application settings and can frequently resolve issues.
If the issue persists, try all remaining steps in the article below.
iCloud: Troubleshooting iCloud Calendar
http://support.apple.com/kb/TS3999
Cheers,
Jason H.