Failed to load mods: Error while loading entity prototype "assembling-machine-1" (assembling-machine): Value must be a list in property tree at ROOT.assembling-machine.assembling-machine-1.crafting_categories
Modifications: Base mod › 5Dim's mod - New Automatization › Standalone Space Age Library › Salt & Chlorine › Combat Mechanics Overhaul › More descriptive tooltips › Krastorio 2 › AAI Industry › Space Exploration › Space Exploration Tweaks › Space Exploration Integration: Library › Brim Stuff Legacy

The only things that I think are unusual are Space Exploration Integration: Library and Space Exploration Tweaks.
Disabling this and Brims Stuff continues loading.

You aren't the first person to report this error with some of the same mods. However, I can't find a "Standalone Space Age Library"; are you sure this is the correct name?

I haven't been able to reproduce the error, but I don't know if that's just because I'm missing that mod or because specific settings are required.

https://mods.factorio.com/mod/um-standalone-space-age-lib
It's required for some of the Space Age DLC standalone mods (adds SA stuff to the base game). Not to be confused with "Space Exploration Integration," which I prefer... but they don't have the "Big Mining Drill" added yet.

Hmmm. I tried installing that one too, and still nothing. Would you be willing to share a save? Like, just get the game to where it's giving the error again, disable Salt & Chlorine, start a new game, and then save immediately.

Be forewarned, I have a LOT of mods, but I got it working by only removing "Salt and Chlorine" and "Space Exploration Integration: Productivity technologies" (separate issue).
Now the real question, how do I share the save? I don't think I can upload it here, so where would you prefer I upload it to?

Ok, I noted the other thread about this and tried loading just Salt and Chlorine, and all the other mods I have installed, just not the intermediaries that this mod goes with, and it worked, so I modified the settings to spawn salt patches instead of modifying the base 1 assembling machine, now I'm trying to load it with the other intermediaries mods, and see if that works.

And...

It worked. So it's that setting that is causing the issue with the other mod(s).
I'm sorry I didn't notice the other thread until now.

Now the real question, how do I share the save?

Most people seem to use google drive. You just have to check the permissions after uploading and make sure it says that anyone with the link can download.

so I modified the settings to spawn salt patches instead of modifying the base 1 assembling machine

I figured that might have something to do with it, but it doesn't seem to be the whole story, since I'm not getting the same error with all the mods you've listed regardless of what that setting is on. I suspect that something on the list is only doing something in the presence of another mod that's not on the list.

https://drive.google.com/file/d/1eD7vMddgGXHawIhpveQ1CmctTsLU9432/view?usp=drive_link

Again, large mod list, sorry about that, but I don't know what is causing it beyond that setting (which fixed it); otherwise, I would minimize the mods for you.

Again, large mod list, sorry about that, but I don't know what is causing it beyond that setting (which fixed it); otherwise, I would minimize the mods for you.

Don't worry about it. It ended up being a very strange set of mods that seem required to invoke the bug. (I'm still not sure why tin and lead are both required, but they are.)

In any case, the core problem is in Brim Stuff Legacy. It moves the "make salt from water" recipe to it's burner chemical plant; fine so far. It removes crafting-from-fluid from AM1 (and burner assembling machines). As a rando player, I'm less than thrilled. But also it does so in a way that is only safe when crafting-with-fluid is the last thing in the list of crafting categories? Then you get this bug.

I think I'll be sending in a PR removing that bit sometime in the not-too-distant future, since I'm not really sure it's a good idea in general; if you want salt from water back in the meantime you can do a quick fix by commenting out the lines

data.raw["assembling-machine"]["assembling-machine-1"]["crafting_categories"][k] = nil

and

data.raw["assembling-machine"]["burner-assembling-machine"]["crafting_categories"][k] = nil

in the data-final-fixes.lua of Brim Stuff Legacy.

Thank you. Always excellent to see a mod developer so willing to find out what's going wrong, and try to fix it.
Amazing work.