Thank you for the report.
This is a weird one, because I'm struggling to reproduce it. You're running into a circumstance that the code should not allow (there's a condition in there specifically to prevent it). So I'm not sure how you've managed to get into this state.
The short version is: when playing with the quality mod, the actual air scrubbers in the world need to be different entities (to allow me to modify the right properties according to quality level). So when quality is enabled a bunch of hidden entities get added to the game. When you place an air scrubber item to build it, a script fires that checks if you're trying to build a non-normal quality air scrubber and then places the appropriate actual entity. Placing a normal quality building gets ignored. Your issue is that script is attempting to place the special hidden version of the air scrubber entity for normal quality. But that entity doesn't exist in the game (because it should just be using the basic plain entity.
I've "fixed" the issue by also adding a hidden entity that's just a copy of the basic one, but with a name that corresponds to the normal quality level. My theory is, your game is asking for an entity with that name, so I'll provide it.
This fix is in version 0.2.2 which I'll be pushing shortly. Please do let me know if it resolves your problem.
I would still like to know how on Earth you've got your game into a state where it's attempting to build the special variant entity for normal quality, so any additional information you could provide would be very helpful. Can you let me know your full mod list? Also, did you add or remove any mods after starting the save file?
Thanks.
