(04:42:16) | [Oxide] 04:42 [Error] Failed to call hook 'OnPlayerConnected' on plugin 'SleeperMark v1.0.24' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.SleeperMark.OnPlayerConnected (BasePlayer player) [0x000df] in <321a17aaf99d41c496462046ed1e664c>:0 
  at Oxide.Plugins.SleeperMark.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00402] in <321a17aaf99d41c496462046ed1e664c>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <98321e516fc1420ea57d4d2088213a59>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ac41dd3599754d448b8c218b34645820>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ac41dd3599754d448b8c218b34645820>:0

I just recieved this error too, when the first player of the day connect about 2 hours ago.