... just woke up with a blinding insight ..
I spent a couple of hours yesterday trying to find "one of those" bugs that are intermittent.
If you haven't seen this one before, It MAY take a little finding.
The example is of course fabricated for this exercise ...
(setq ms (vla-get-modelspace
(vla-get-activedocument (vlax-get-acad-object))
)
oPline (vlax-invoke ms
'AddLightweightPolyline
'(0.0 0.0 200.0 0.0 200.0 100.0 0.0 100.0)
)
xoPline (vlax-invoke ms
'AddLightweightPolyline
'(0.0 0.0 200 0.0 200 100 0.0 100)
)
)
The input vertex data needs to be reals. Ints are NOT acceptable.
When you stop to think about it in hindsight, the ActiveX method requires a double, so ..
tuck this away, it may save your sanity one day