(21:40:46) | Failed to call hook 'ViewBackpack' on plugin 'Backpacks v3.0.2' (NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.Backpacks.ViewBackpack (BasePlayer player, System.String cmd, System.String[] args) [0x000c1] in :0
at Oxide.Plugins.Backpacks.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0083f] 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

same problem :(

hello i get this message with some players when i want to look into the backpack with others it works

Failed to call hook 'ViewBackpack' on plugin 'Backpacks v3.0.2' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Backpacks.ViewBackpack (BasePlayer player, System.String cmd, System.String[] args) [0x000c1] in <8a845f8bcbd145d58aef1d2fef742c74>:0 
  at Oxide.Plugins.Backpacks.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0083f] in <8a845f8bcbd145d58aef1d2fef742c74>: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​

Hawker

hello i get this message with some players when i want to look into the backpack with others it works

Failed to call hook 'ViewBackpack' on plugin 'Backpacks v3.0.2' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Backpacks.ViewBackpack (BasePlayer player, System.String cmd, System.String[] args) [0x000c1] in <8a845f8bcbd145d58aef1d2fef742c74>:0 
  at Oxide.Plugins.Backpacks.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0083f] in <8a845f8bcbd145d58aef1d2fef742c74>: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​

Can you send me the backpacks file from the data directory for that user?

This should be fixed with 3.0.3. Thanks @Hawker for providing additional help.