Particles/additive

I want to do a trace line (visible path) of unit. For example, as is done in C&C Tiberian Sun. Units is a rage pixel sprite. trace line is a LineRenderer. To see a LineRenderer on my scene i add next code (find in web):

LineRend.material = new Material(Shader.Find("Particle/Additive"));

When “Play” button pressed in IDE all ok. When i try to build project using “Build & Run” i have a problem: my line renderer is “invisible” but all other works. What i do wrong?

Solved.
There was an error in the code and for this reason, the function Update finished its work at the beginning.