Did a little testing to add to this because I suspected it had something to do with the weapon present in the extra equipment slot.
- When following the above steps, the issue regarding craft-failure occurred if the crafting method (such as Weaving, Magic Craft, Hillwen Engineering) can be activated with objects in your hands (such as a blade, oak wand, or spanner/hammer), and you attempt to craft a bare-handed recipe.
- The issue also occurred if I contained the correct tool in my hands prior to attempting to change equipment slot to a bare-handed slot after following the above steps, and then attempt to craft an item that requires the tool. (Presumably, I am no longer holding the correct tool.)
- If the crafting method requires bare hands (has no associated tool) and I recreate the scenario with a broken weapon in my primary slot, and no weapon/tool in my secondary slot OR Extra Equipment slot, an error message occurs
Empty both of your hands in order to craft, despite my hands both visually being empty. This occurs even if my Extra Equipment slot has no weapon and my hands are empty, but a broken weapon is present within my Primary Weapon slot.
Note: The broken weapon was located in my Primary Slot (I), and I predominantly kept my Secondary Slot (II) empty and as my active slot.
I have not tested this with the broken weapon in my secondary slot. I have a theory that this has to do with the primary weapon slot and how, after equipment swapping, Mabinogi tends to default back to the primary slot, but fails to do so visually if the equipment swap fails to occur.
This issue did not occur when testing with broken armour, however in this instance, all of my weapon slots involved were empty. This leads me to believe the gear within the Primary Slot is the culprit.
So, avoid having anything in both of your slots when doing expensive crafts. 