Need help on a triggered aura

Hi I'm having a prblem with this trigger:
Soul Drain Aura
Events
Time - Every 1.00 seconds of game time
Conditions
Actions
Unit Group - Pick every unit in Souldrain and do (Actions)
Loop - Actions
Unit Group - Remove all units of Souldrain from Souldrain
Unit Group - Add all units of (Units within 900.00 of (Position of (Triggering unit)) matching (((Picked unit) belongs to an enemy of (Owner of Dark Ranger 0000 <gen>)) Equal to True)) to Souldrain
Unit Group - Pick every unit in Souldrain and do (Actions)
Loop - Actions
Unit - Set life of (Picked unit) to ((Life of (Picked unit)) - 1.00)

the problem is that it does NOTHING. It doesn't do any damage at all to them like it should. Also, how do I make it so it reqrueis the aura present before it does the actions? I'm assuming conditions but don't know what conditions to put in.

This is actually pretty subtle, I dont blame you for not spoting it. Look here:

Unit Group - Add all units of (Units within 900.00 of (Position of (Triggering unit)) matching (((Picked unit) belongs to an enemy of (Owner of Dark Ranger 0000 <gen>)) Equal to True)) to Souldrain


More specifically the part in bold. THere is no triggering unit, so therefore the whole trigger does nothing. You might want to change this to Dark Ranger 0000 or something.

Doh! Thanks for pointing that out, I'm so used to having "Unit begins casting an ability". Thanks for the help I'll go test it out right now!

Actually you could just use permanent immolation instead of a trigger