@blanchg So, as I said by moving everything on an external drive I solve the errors I get. I assume that my windows system it's the reason due to permission issues as Burnin said.
Now, I've tested in a simple scene and I didn't have problems by launching the render, everything ran smooth. On the other side for a good usability, I think that real-time preview of the scene (like in max) it's necessary especially because right now the simple material preview doesn't update correctly when you play with values. Also, editing materials can be done in the material editor and the node editor, but in the material editor things like glossy texture aren't available like instead does in the node editor.
So shading usability along with the few node input to me feels the most undeveloped area.