In the Factorio Version 2.1.20 i get the following error message.
I disabled all other mods to test, if there was a mod incompatibility. With only the Auto-Loader Mod enabled i get the error message on creating a new world:

The mod Auto-Loader (1.2.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event auto-loader-chest::on_init()
LuaItemPrototype doesn't contain key fuel_category.
stack traceback:
    [C]: in function '__index'
    __auto-loader-chest__/control.lua:58: in function 'build_caches'
    __auto-loader-chest__/control.lua:427: in function <__auto-loader-chest__/control.lua:426>

And this on loading the existing save game with other Mods enabled:

The mod Auto-Loader (1.2.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event auto-loader-chest::on_load()
LuaItemPrototype doesn't contain key fuel_category.
stack traceback:
    [C]: in function '__index'
    __auto-loader-chest__/control.lua:58: in function <__auto-loader-chest__/control.lua:51>

Fixed!

Thank you so much for reporting this, and taking the time to boot the game with just this mod to isolate the error.

Also, sorry for the sloooow response, I didn't see a notification about the forum posts. I'm going to write a program to proactively alert me when things come up. Have fun!