Failed to run a 2.00 timer in 'ZoneManager v2.5.10' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ZoneManager.CheckSpawnedEntity (BaseNetworkable entity) [0x00149] in <b195fbdc2312438a8db24d00df07aefb>:0 
  at Oxide.Plugins.ZoneManager+<OnEntitySpawned>c__AnonStorey0.<>m__1 () [0x00000] in <b195fbdc2312438a8db24d00df07aefb>:0 
  at Oxide.Core.Libraries.Timer+TimerInstance.FireCallback () [0x00018] in <4452f821def6406d834e4149849fe7ea>:0 

Saw this spammed a bunch in the logs

Merged post

Also does this on plugin unload

Failed to call hook 'Unload' on plugin 'ZoneManager v2.5.10' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ZoneManager.OnBuildingExitZone (Oxide.Plugins.ZoneManager+Zone zone, BaseCombatEntity entity, System.Boolean all) [0x000e5] in <b195fbdc2312438a8db24d00df07aefb>:0 
  at Oxide.Plugins.ZoneManager.OnZoneDestroy (Oxide.Plugins.ZoneManager+Zone zone) [0x00092] in <b195fbdc2312438a8db24d00df07aefb>:0 
  at Oxide.Plugins.ZoneManager.Unload () [0x0006b] in <b195fbdc2312438a8db24d00df07aefb>:0 
  at Oxide.Plugins.ZoneManager.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fdb] in <b195fbdc2312438a8db24d00df07aefb>: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.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0 ​

I just seen the same thing (2nd Error listed above) in my RCON Console. was gonna post the error til I saw this.

yup +1, can't unload this plugin :D

(19:04:03) | Failed to call hook 'Unload' on plugin 'ZoneManager v2.5.14' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ZoneManager.OnEntityExitZone (Oxide.Plugins.ZoneManager+Zone zone, BaseCombatEntity entity, System.Boolean all) [0x000f2] in :0 
  at Oxide.Plugins.ZoneManager.OnZoneDestroy (Oxide.Plugins.ZoneManager+Zone zone) [0x00092] in :0 
  at Oxide.Plugins.ZoneManager.Unload () [0x0006b] in :0 
  at Oxide.Plugins.ZoneManager.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00fca] in :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.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

That error just means that something in that hook call failed when it was unloading, not that the plugin failed to unload.

yep got the same thing. nice to hear it isnt a huge issue.... :D

strange is that i have this error only on 1 (from 3) servers... maybe some other plugin is the problem hmm

Still happening in the latest version too