The problem is not LUA but the way LUA is implemented.
1. The built-in script editor is bad. Yes, I use a separate "IDE" (Notepad ++) but to get it working I need to close and reload the script in Sandbox every time I make a change to make it work.
2. I want to know why, and even more importantly, where my script is crashing. A report saying "mymodel.lua crashed on line 86" would be the bare minimum.
3. When one of my scripts has crashed, this should not be able to effect any other scripts. If a model's script is failing this should not affect the loading of my scene or any other scripts. (This would be less of a problem of course if I actually knew what caused the failure in the first place, see point 2.)