Failed to call hook 'OnStructureUpgrade' on plugin 'EnhancedHammer v2.0.6' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.EnhancedHammer+PluginData+Preference.UpdateGradeTimer () [0x00027] in :0
  at Oxide.Plugins.EnhancedHammer+PluginData+Preference.DoGrade (BuildingBlock block, System.Boolean suppressMessages) [0x00000] in :0
  at Oxide.Plugins.EnhancedHammer.OnStructureUpgrade (BuildingBlock block, BasePlayer player, BuildingGrade+Enum grade) [0x00055] in :0
  at Oxide.Plugins.EnhancedHammer.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x001d8] in :0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <3e46d2a997e94a3cb08cf065508cd483>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <1fe782f4b27a43ae85d29ebb2d56c007>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <1fe782f4b27a43ae85d29ebb2d56c007>:0

@LR300 did you unload the plugin before this happened or something? I doubt it can happen on its own.

All I did was leave the plugin and it was giving errors in console, I just reinstalled it and it fixed it.