Apple event handler failed

I used to use an Apple script that deletes all display alarms of every event of a calendar.

tell application "Calendar"
	tell calendar "GOA"
		set the_events to every event
		repeat with an_event in the_events
			tell an_event
				-- do something with every event
				delete every display alarm
				make new display alarm at end of display alarms with properties {trigger interval:-300}
			end tell
		end repeat
	end tell
end tell

This script stopped working and throws the error

in the line where the display alarm is deleted.
And even if I comment out this line the following line isn’t working either. The error is

Any help is deeply appreciated (since there are lots of events in this calendar :wink: ).

Model: Macbook Pro 2015
AppleScript: 2.7
Browser: Safari 605.1.15
Operating System: macOS 10.14