I get this error when using the shopfile command, anyone know why?

Failed to call hook 'cmdshopfile' on plugin 'ItemCostCalculator v1.0.1' (ArgumentException: An item with the same key has already been added. Key: bleach)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].TryInsert (TKey key, TValue value, System.Collections.Generic.InsertionBehavior behavior) [0x000c1] in :0
  at System.Collections.Generic.Dictionary`2[TKey,TValue].Add (TKey key, TValue value) [0x00000] in :0
  at Oxide.Plugins.ItemCostCalculator.GetItemCost () [0x00055] in :0
  at Oxide.Plugins.ItemCostCalculator.cmdshopfile (ConsoleSystem+Arg arg) [0x00000] in :0
  at Oxide.Plugins.ItemCostCalculator.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x001fa] in :0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0