Whenever I place a factory building, I get this error message;

The mod Factorissimo2 caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Factorissimo2::on_built_entity (ID 6)
Index out of inventory bounds.
stack traceback:
Factorissimo2/control.lua:354: in function 'update_overlay'
Factorissimo2/control.lua:578: in function 'create_factory_exterior'
Factorissimo2/control.lua:748: in function <Factorissimo2/control.lua:740>
stack traceback:
[C]: in function 'index'
__Factorissimo2/control.lua:354: in function 'update_overlay'
Factorissimo2/control.lua:578: in function 'create_factory_exterior'
Factorissimo2/control.lua:748: in function <Factorissimo2/control.lua:740>

I have no clue what this is, but I would assume at first it is an overlapping error?

This is an error that happens because you have installed some mod that changes inventory sizes. The factory overlay entities should have 4 inventory slots, but the mod changes them to have 1. Uninstall the inventory size changer, or adjust its settings so it no longer changes the affected inventory sizes.

Alternatively, update Factorio to 0.18 (if your mods are all available for 0.18), because this crash was fixed in Factorissimo2 version 2.4.1 for Factorio 0.18.

Ah ok.

Thank you magma!