Looks like you broke something else.
841.474 Error MainLoop.cpp:1284: Exception at tick 23940: The mod RPG Items (0.21.2) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event m-rpg_items::on_nth_tick(60)
m-rpg_items/control.lua:523: attempt to index field 'rpgitems_item_gui' (a nil value)
stack traceback:
m-rpg_items/control.lua:523: in function <m-rpg_items/control.lua:499>
841.474 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod RPG Items (0.21.2) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event m-rpg_items::on_nth_tick(60)
m-rpg_items/control.lua:523: attempt to index field 'rpgitems_item_gui' (a nil value)
stack traceback:
m-rpg_items/control.lua:523: in function <m-rpg_items/control.lua:499>"