rendering problem

trying to render a material using v ray , i used refraction at abouot 60 % so some of the colour still shows but when i render the material instead of coming up as a grey transparent material it comes up as a sort of checkerboard ie some parts completely clear then completely grey boxes thoughout the material , has anyone experienced this ?? is there a way to fix is using vray or 3dsmax or is this just something wrong with my PC ??

Thanks in advance

Sounds like flipped normals, is it modeled out of max?

It happend to me once. I think it has something to do with imported geometry.
There’s a thread here somewhere.

also may occur when two faces are in the same plane ie on top of each other