Unknown event opening Skype periodically
Temporary Solution, however it disables iCal.

put sudo launchctl list | grep CalendarAgent into Terminal and give it access to stop CalendarAgent.

If you attempt to open iCal with CalendarAgent disabled, it will attempt to update it's calendars then crash.

To restore CalendarAgents, type launchctl load -w /System/Library/LaunchAgents/com.apple.CalendarAgent.plist into Terminal and enter your password.

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