Failed to call hook 'DanceCommand' on plugin 'Dance v1.1.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Dance.DanceCommand (BasePlayer player, System.String command, System.String[] args) [0x00106] in <b83ca1e7bcdc40d6ba811ca949e9180f>:0 
  at Oxide.Plugins.Dance.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x000b9] in <b83ca1e7bcdc40d6ba811ca949e9180f>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <31122a27a2414cd799150f8677cf39d4>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

Fix it you need to delete the old dance.json from config folder