The file paths described in the tutorials online do not match the file directories that are downloaded from the help>'Download Tutorials and Examples' tab in CityEngine Advanced 2016.0
I've only checked this for Tutorial 6, but i expect that the problem exists in other tutorials...
On the site the path is given as:
frontdoor_tex = "facade/shopdoor.tif"
wall_tex = "facade/brickwall.jpg"
dirt_tex = "facade/dirtmap.15.tif"
roof_tex = "roof/roof.tif"
but the correct paths from the downloaded assets are:
frontdoor_tex = "facades/textures/shopdoor.tif"
wall_tex = "facades/textures/brickwall.jpg"
dirt_tex = "facades/textures/dirtmap.15.tif"
roof_tex = "roofs/roof.tif"