If you edit a render material via PARTproject → Tabbed page General → Render materials [Render Materials] and declare it as a texture label [Texture label] by activating the checkbox, the fields Color texture and Normal map [Normalmap] must be filled in. Otherwise an error message appears.
Further information on the render properties can be found in the chapter Section 5.9.2.8, “Menu item: Render properties ” in eCATALOG 3Dfindit.