If you use the material basic_trans_spec, it will require you to add a normTex, which the name does not imply. Solution : Do not load the norm texture.
Only files using it are:
art/actors/units/celts/wolfhound.xml: <material>basic_trans_spec.xml</material>
art/materials/basic_trans_parallax_spec.xml: <alternative material="basic_trans_spec.xml" quality="8"/>
Which doesn't have a norm texture