Animate VrayBlendMtl inside Maya


Hi everyone, Im working with Vray 3.6 inside Maya.
Im not expert with Vray, but I need fast Vray renders for this project, also is a great rendering aplication.

The problem is that I actually have made a simple animation beetween two materials using a VrayBlendMtl. I keyframed black for first of these materiales in frame 1 using Blend Amount and white for the other material in frame 25.

I cant see the change beetween materials in final animation when I use Render Sequence. If I use VFB manualy for make some static renders and jump beetween frames I can see the change.

Im sure that problem its a silly checkbox in the Render Setting but im not finding solution at any documentation.