How do I create calender alarms using Applescript (using OSX Yosemite/Mavericks)?

I have an Applescript here that triggers when an ICS file has been dropped into a folder. All it does it imports the ICS file into the Calendar and then create alarms for each calendar entry.

This was working fine on Mountain Lion. But hasn't been working since Mavericks/Yosemite. The macmini (bought late 2014) it's installed on can only use Yosemite. I cannot install anything else.

The calendar entries are being imported. But no alarms are being created.

This is code I use to add the alarm. I didn't include the code that imports the ICS file but that part is working.

Code:

tell application "Calendar"
	tell calendar "Home"
		delay 1
		set myevents to every event
		
		repeat with oneevent in myevents
			tell oneevent
				set mysummary to summary
				display dialog mysummary
								
				make new display alarm at end with properties {trigger interval:-30}
			end tell
		end repeat					
	end tell
end tell

As you can see from the code, I am displaying the summary for the event just as a test. I just want to find out it's opening the correct event.

I've looked/searched for examples/documentation on the topic but hardly find anything recent (i.e. Mavericks and above).

Any ideas on how to fix my problem? Thanks a lot