Thanks everyone!
File names in Val file are OK, files are present.
@Anvar1061 your linked post refere to a splitted half unit with wrong textures; sadly, this is a different scenario.
@Hebe Vollmaus this is really interesting. Yes, 'Damage_metal_a.tga' appear to be involved...
I've read your linked post also, same problem, bingo, but where is the solution?
Best regards,
Vd