This works without errors
ActorCreate(null, "Beam", "ColossusAttackBeam", "::global.Launch", "::global.Impact");
Which looks as if it creates a Colossus Attack Beam actor and works without error but I don't know where to go from here
Well, what are you trying to do exactly?
Beams are handled in the actor events, using a channeled effect (persistent) to handle when to turn the beam on and off, along with the location of where the beam is aiming for. With your above scenario, I'm not sure how you're giving it a location to fire to, nor if it would even fire with a manual actor creation like that. Even if it did, I'm not sure it would know when to turn itself off, minus you telling the actor to destroy itself (or it may just do that automatically since it's an orphan, I think most beams script for that..).
It would probably be more realistic to trigger a persistent effect to channel that turns the beam on for a set duration, maybe even add a behavior to your beam shooting point if you want to do it timed via triggers, and have the behavior being removed as a way to turn off the effect.. but this is theorycraft for a scenario I'm entirely guessing about. XD Not sure behaviors can "channel" an effect or not.
Can always do the good ol' invisible unit channeling.
The idea is to use only triggers to create a beam and to avoid effects. The linked topic already contains some approaches on how to specify the launch and impact location and how to pass orders to the beam.
One tiny problem however: It doesn't work.