Warning: Filename not defined in 'sounds.motor(3)'. Ignoring it!

[SGA-modding]

Hi, can you tell me about the error Warning: Filename not defined in 'sounds.motor(3)'. Ignoring it! What does it mean and how to fix it?

[Achimobil]

In the XML there are sounds and the sounds has 4 or more sub notes called "motor". counting in that case starts with 0, so the 4th motor node has no filename and the defined motor sound require a filename.