Failed to run a 0.50 timer in 'TcOptions v1.0.8' (NullReferenceException: Object reference not set to an instance of an object)
  at Item.MoveToContainer (ItemContainer newcontainer, System.Int32 iTargetPos, System.Boolean allowStack, System.Boolean ignoreStackLimit, BasePlayer sourcePlayer, System.Boolean allowSwap) [0x0000c] in <863b8d7ccbed46e59f3aaaa52fa75203>:0

  at Oxide.Plugins.TcOptions.PopulateItems (System.Collections.Generic.List`1[T] items, ItemContainer itemContainer) [0x0008e] in <cd89dfb08c7d4f4d9d02959f53db4438>:0

  at Oxide.Plugins.TcOptions.Apply (BuildingPrivlidge buildingPrivilege, Oxide.Plugins.TcOptions+Settings settings, BasePlayer player) [0x0001a] in <cd89dfb08c7d4f4d9d02959f53db4438>:0

  at Oxide.Plugins.TcOptions+<>c__DisplayClass6_0.<OnEntityBuilt>b__0 () [0x00000] in <cd89dfb08c7d4f4d9d02959f53db4438>:0

  at Oxide.Core.Libraries.Timer+TimerInstance.FireCallback () [0x00018] in <15f61ddda771464d8246ebdce8ff4811>:0

i need more contex please . is it doing it every time you place a tc ? 

When I have a lot of people on server

i get the exact same thing

"

Failed to run a 0.50 timer in 'TcOptions v1.0.8' (NullReferenceException: Object reference not set to an instance of an object)
  at (wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Item.MoveToContainer_Patch1(Item,ItemContainer,int,bool,bool,BasePlayer,bool)
  at Oxide.Plugins.TcOptions.PopulateItems (System.Collections.Generic.List`1[T] items, ItemContainer itemContainer) [0x0008e] in <bfba1352eb044009aa42d681ace256ca>:0

  at Oxide.Plugins.TcOptions.Apply (BuildingPrivlidge buildingPrivilege, Oxide.Plugins.TcOptions+Settings settings, BasePlayer player) [0x0001a] in <bfba1352eb044009aa42d681ace256ca>:0

  at Oxide.Plugins.TcOptions+<>c__DisplayClass6_0.<OnEntityBuilt>b__0 () [0x00000] in <bfba1352eb044009aa42d681ace256ca>:0

  at Oxide.Core.Libraries.Timer+TimerInstance.FireCallback () [0x00018] in <15f61ddda771464d8246ebdce8ff4811>:0"

it dies here:

TcOptions.PopulateItems → Item.MoveToContainer

TC places successfully, then 0.5 seconds later TC Options attempts to insert one of the configured items and gets a null reference

Like i said i need more info as i cant replicate it on my end . show what your config looks like please