SteamInventory error when players connect

When connect the players to the server, players get the following error

Code:

DATA IS NULL!
[SV_RPCMessage] updatesteaminventory - Exception has been thrown by the target of an invocation.
NullReferenceException: Object reference not set to an instance of an object
SteamInventory.UpdateSteamInventory (RPCMessage msg)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters)
BaseEntity+<FindRPCMessage>c__AnonStorey24.<>m__56 (RPCMessage rpcMsg)
BaseEntity.SV_RPCMessage (UInt32 nameID, Network.Message message)
UnityEngine.Debug:LogException(Exception)
BaseEntity:SV_RPCMessage(UInt32, Message)
ServerMgr:OnRPCMessage(Message)
ServerMgr:OnNetworkMessage(Message)
Network.Implementation.Raknet.Server:ConnectedPacket(RaknetConnection)
Network.Implementation.Raknet.Server:Cycle()
ServerMgr:Update()

 

I also have this problem.