Does it really make sense to assign top and left without a container in which to display a line?

Try this:

_screen.AddObject("x","line")
_screen.X.Top = 180
? _screen.X.Top 
_screen.X.Top = 180.00
? _screen.X.Top

ox= createobject("form")
ox.addobject("x","line")
ox.X.Top = 180
? ox.X.Top 
ox.X.Top = 180.00
? ox.X.Top