Sorry for the late reply TheBen...
First you need to fix the script Game_Interpreter...go to line 750 where it says
actor = $game_actors[@parameters]
actor = $game_actors[@params]
Change the first line(750) to line 751 or delete the line entirely.
Now that we have that fixed...
You need to make a common event so it can update the armor/weapon in your inventory at all times.
Name Common Event Weapons/Armor.
=Create a wait 30 frames in the beginning to prevent lag. It will update within the second so it shouldn't effect the game at all.
=Create a "Control Variables..." Set
The Variable "Weapon" I.E. Iron Sword...to Item In Inventory
. It should set the variable to the amount of Iron Swords you have, then do that for all your equipment/weapons. All In that one common event.
Hope that helps...if not tell me and I'll figure it out