Console has been spamming this error. Possible caused server crash, can anyone help what it means? I also had sellingitems disabled from UI ever since I started using serverrewards I'm not sure why its causing an error.

Failed to call hook 'cmdSellItem' on plugin 'ServerRewards v0.4.73' (KeyNotFoundException: The given key was not present in the dictionary.)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x0001e] in <fb001e01371b4adca20013e0ac763896>:0 
  at Oxide.Plugins.ServerRewards.SellItem (BasePlayer player, System.String shortname, System.UInt64 skinId, System.Int32 amount) [0x00011] in <88d9cf4752894077a1fc566a24ad873d>:0 
  at Oxide.Plugins.ServerRewards.cmdSellItem (ConsoleSystem+Arg arg) [0x00062] in <88d9cf4752894077a1fc566a24ad873d>:0 
  at Oxide.Plugins.ServerRewards.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fda] in <88d9cf4752894077a1fc566a24ad873d>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <09575a60985045248bcb43b20faeeb99>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <bae5f1223fce49c493b01571c99dce02>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <bae5f1223fce49c493b01571c99dce02>:0