This happend after I updated the plugin

Failed to call hook 'OnServerInitialized' on plugin 'GUIShop v1.8.6' (ArgumentNullException: Value cannot be null.
Parameter name: key)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in <fb001e01371b4adca20013e0ac763896>:0
  at System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) [0x00000] in <fb001e01371b4adca20013e0ac763896>:0
  at Oxide.Plugins.GUIShop.LoadImages () [0x00029] in <e3e0b529bb8b45bab44f4059a26fa38e>:0
  at Oxide.Plugins.GUIShop.OnServerInitialized () [0x00049] in <e3e0b529bb8b45bab44f4059a26fa38e>:0
  at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fbd] in <e3e0b529bb8b45bab44f4059a26fa38e>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0

Please add me on discord Khan#8615 to send me your config and what version did you update from? 

Failed to call hook 'OnServerInitialized' on plugin 'GUIShop v1.8.8' (ArgumentNullException: Value cannot be null.
Parameter name: key)
at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in <fb001e01371b4adca20013e0ac763896>:0
at System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) [0x00000] in <fb001e01371b4adca20013e0ac763896>:0
at Oxide.Plugins.GUIShop.LoadImages () [0x00029] in <4c89d9fbbbcd43fd9bf8261b5af60a8f>:0
at Oxide.Plugins.GUIShop.OnServerInitialized () [0x0005a] in <4c89d9fbbbcd43fd9bf8261b5af60a8f>:0
at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x01069] in <4c89d9fbbbcd43fd9bf8261b5af60a8f>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0

khan

So you didn't follow the update notes? and jumped straight into the latest.. well then ya your gonna get that error no matter what. I can update your config but not unless you send it either via discord or as a link. 

I dont think i did no. LOL, i did revert back to the old plugin version while it was figured out. Add me on discord Danny!#0007 i will send it you there :) 

Failed to call hook 'OnServerInitialized' on plugin 'GUIShop v1.8.93' (ArgumentNullException: Value cannot be null.
Parameter name: key)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in <fb001e01371b4adca20013e0ac763896>:0
  at System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) [0x00000] in <fb001e01371b4adca20013e0ac763896>:0
  at Oxide.Plugins.GUIShop.LoadImages () [0x00029] in <90c84406518649ab9824f37003e948ac>:0
  at Oxide.Plugins.GUIShop.OnServerInitialized () [0x0005a] in <90c84406518649ab9824f37003e948ac>:0
  at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fd3] in <90c84406518649ab9824f37003e948ac>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0

Failed to call hook 'OnServerInitialized' on plugin 'GUIShop v1.8.93' (ArgumentNullException: Value cannot be null. Parameter name: key) at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in :0
at System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) [0x00000] in :0
at Oxide.Plugins.GUIShop.LoadImages () [0x00029] in <6d85c02e03ee4146988d8d39dae81376>:0
at Oxide.Plugins.GUIShop.OnServerInitialized () [0x0005a] in <6d85c02e03ee4146988d8d39dae81376>:0
at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fd3] in <6d85c02e03ee4146988d8d39dae81376>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in :0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in :0

Failed to call hook 'OnServerInitialized' on plugin 'GUIShop v1.8.93' (ArgumentNullException: Value cannot be null.
Parameter name: key)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) [0x00008] in <fb001e01371b4adca20013e0ac763896>:0
  at System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) [0x00000] in <fb001e01371b4adca20013e0ac763896>:0
                                                                                   25kb/s in, 199kb/s out
  at Oxide.Plugins.GUIShop.LoadImages () [0x00029] in <31e72e2b78c240c6817d96f39d21f884>:0
  at Oxide.Plugins.GUIShop.OnServerInitialized () [0x0005a] in <31e72e2b78c240c6817d96f39d21f884>:0
  at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fd3] in <31e72e2b78c240c6817d96f39d21f884>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0

I want to know the cause of the error and a solution.

This issue has been patched. create a new thread with the GUIShop version if still happening..