Try applying a normal modifier, then another normal modifier (not sure which version of max you're using but in 2014 i have this fucked up issue where if i uncheck "flip normals" in the normal modifier, the modifier doesn't actually reset the normals, so i have to apply two modifiers so it flips the normals twice... it's…
Like wirrexx said, redo the UV's on the low poly. Corrupt UV's can happen if you edit a model below the unwrap modifier. Sometimes the UV's will *look unaltered, but what happened internally is every UV Vertex was bumped over one number. Same thing happens with the Skin Modifier.