Failed to initialize plugin 'FuelGauge v0.1.6' (NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.FuelGauge.LoadVariables () [0x0001e] in <4efb7fc0a7fb4a65a2f68950bda26273>:0
at Oxide.Plugins.FuelGauge.Init () [0x00012] in <4efb7fc0a7fb4a65a2f68950bda26273>:0
at Oxide.Plugins.FuelGauge.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x000e5] in <4efb7fc0a7fb4a65a2f68950bda26273>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
at Oxide.Core.Plugins.CSPlugin.HandleAddedToManager (Oxide.Core.Plugins.PluginManager manager) [0x00043] in <4452f821def6406d834e4149849fe7ea>:0
(10:53:03) | Unloaded plugin Fuel Gauge v0.1.6 by Oryx

scratch that, I got it - sorry

You forgot to delete the config file.

So delete the config file and then the plugin will work? Or delete the old version of the plugin and config file and then load the new one?

Some plugins after updating them you need to delete the old config file in you'r case yes you need to delete. The new version should be fine now. Make sure its version 0.1.7

Failed to initialize plugin 'FuelGauge v0.2.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.FuelGauge.LoadVariables () [0x0001e] in <2fed3bdb60664332af314779e0cd64bc>:0 
  at Oxide.Plugins.FuelGauge.Init () [0x00012] in <2fed3bdb60664332af314779e0cd64bc>:0 
  at Oxide.Plugins.FuelGauge.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x000e5] in <2fed3bdb60664332af314779e0cd64bc>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.CSPlugin.HandleAddedToManager (Oxide.Core.Plugins.PluginManager manager) [0x00043] in <4452f821def6406d834e4149849fe7ea>:0 

You need to delete your config file and reload the plugin