the beam component is expecting a curve, but you input a list of points instead.
Grasshopper is quite intelligent in converting data types on the fly, but as you see in this case, the conversion from a list of Points to Curve is not implemented.
I followed the example precisely and it wasn't functioning correctly. I also went through a few other examples and they seem to fail as well. It would be nice to have the example script to reference and compare to from Graphisoft.