A guy report this on our server:

I think the correct way to define the open sound in Factorio 0.18.X is:

local sounds = require("prototypes.entity.demo-sounds") -- At the beginning of the file
...
open_sound = sounds.gate_open -- In the entity definition
...

U should change this in the entity prototype definition file

Hm, I am actually using Natural evolution as well without issues. But I guess you are right: It should be safer to use the predefined lists of sounds instead of referencing them directly, which should also future-proof it against all potential changes to the base-files in coming updates.
I will patch it in a new version.

https://gyazo.com/ae1af37314c369eac51d404750a9a7c2

OK, I now see what's going on: The gate-sounds I'm trying to use for the opening and closing effects of the transceiver didn't exist in Factorio version <=0.18.13. I've now fixed this by specifying that you need at least 0.18.18 to run the mod. This was probably also the root-cause for the original issue that was raised.

Thank Khalcifer for your post.

the error appears if you put all required items
https://gyazo.com/532ecdc64e647a96e5ec54c916561f41

Hm, I see. Are you by any chance using multiple transceivers at once? I wasn't able to reproduce this but I believe I know where this might stem from: Once you insert all the required items the building is replaced with a new one of a different type. This modifies the list which is being iterated trough and which is mentioned in the error message you posted.
I've uploaded a new version which should not contain this possible issue anymore. Thanks again.

works for now, I will test