[Error] Failed to call hook 'Unload' on plugin 'RemoverTool v4.3.30' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.RemoverTool.SaveDebug () [0x00015] in <7a5a65d7bef7468e8cd3cf3a13ea2811>:0 
  at Oxide.Plugins.RemoverTool.Unload () [0x000b8] in <7a5a65d7bef7468e8cd3cf3a13ea2811>:0 
  at Oxide.Plugins.RemoverTool.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0045d] in <7a5a65d7bef7468e8cd3cf3a13ea2811>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <9882f28dc2204b4dba514a9ad18f5042>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <9882f28dc2204b4dba514a9ad18f5042>:0 

Solved

Is there an error in the code? Please let me know, thanks!

Too many plugin have the same issue when server start so it's a server issue maybe (idk really) nd now i cannot help you, ive no access to this server.