Sorry, I know "sometimes" is very poor...
I find some differences now:

1.- create an instance of Curve (Basic categorie at Object Catalog)
2.- Halo > Menu > Show handles with it
3.- open its Viewer and look for "vertices", you'll find:
remove all vertices but cursor
Run this command once
    then  I get an EvaluationError

1.- create an instance of Curve (Basic categorie at Object Catalog)
2.- open its Viewer and look for "vertices", you'll find also:
remove all vertices but cursor
Run this command once
3.- now that you have a black point, get (complicated without easySelection ON, perhaps easySelection could have a keyboard shortcut) its Halo and clic on  Menu > Show handles
4.- look for: remove all vertices but cursor and run this command once
    then  I get an PreDebugWindow

1.- create an instance of Curve (Basic categorie at Object Catalog)
2.- Halo > Menu > Show handles with it
3.- open its Viewer and look for "vertices", you'll find also:
remove all vertices but cursor
Run this command once
4.- now that you have a blue circle and a orange triangle, clic on the triangle: OrderedCollection error
or try to move the object from the blue circle: OrderedCollection error

regards