HELP! Materials turned black in vray 3.4 for rhino when rendering

i was working on a render and suddenly some materials that applied on imported mesh models, turned black- All materials are 2 sided and i think problem is from loading textures , materials used to be fine but mid render turned black and stayed that way
l had the same problem before but then it turned black on materials applied on nerbs models and i fixed it by re building the material using different textures and it worked
i have other mesh models in the scene that same materials work on them


You have to explode the block mesh and apply material then join it again .