The tip to set component error="true" in the UserAction worked a treat. It allowed the syntax error in the UserAction to bubble to the surface so I could fix it.

The the issue is getting a hold of the camera.

I thought running the script from the ACP console would attach it to Util.ScriptCamera. Not so much. So I have:
try {
cam= Util.ScriptCamera;
} catch(e) {
cam= new ActiveXObject("MaxIm.CCDCamera");
cam.LinkEnabled= true;
I assume that when this executes from within the Scheduler stack the first alternative will work. I'm running standalone so need to grab the camera directly.

But now I'm getting an object error on cam.GuiderFilterNames
Object error.
Issue of dealing with an array??

Thx for the help!