gs.eventQueueScheduled takes 5 parameters:

1. event name
2. current object
3. parm1
4. parm2
5. date/time when the event should fire

It looks like you only have 4 parameters.

If you want it to send 30 minutes before the date/time identified in Next Action Date Time, you should also subtract 30 minutes from it. See this thread on how to do that: Add minutes to time field