Exception in callback: Failed to activate observer for behaviour "nomad"

i am trying to great vuforia model target, but i got this error when i setup more one target in the same scene.

The error:

Exception in callback: Failed to activate observer for behaviour 'nomad_creo'
UnityEngine.Debug:LogErrorFormat (string,object[ ])
Vuforia.Internal.Utility.UnityLogger:LogError (string,object[ ])
Vuforia.Internal.Utility.Log:Error (string,object[ ])
Vuforia.Utility.ExtensionMethods.DelegateHelper:InvokeDelegate (System.Delegate,object[ ])
Vuforia.Utility.ExtensionMethods.DelegateHelper:InvokeWithExceptionHandling (System.Action)
Vuforia.Internal.Core.Engine:OnStart ()
Vuforia.Internal.Core.Engine:Start (System.Action)
Vuforia.Internal.Core.Engine:Start ()
Vuforia.VuforiaBehaviour:VuforiaInitialized (Vuforia.VuforiaInitError)
System.Delegate:smile:ynamicInvoke (object[ ])
Vuforia.Utility.ExtensionMethods.DelegateHelper:InvokeDelegate (System.Delegate,object[ ])
Vuforia.Utility.ExtensionMethods.DelegateHelper:InvokeWithExceptionHandling<Vuforia.VuforiaInitError> (System.Action`1<Vuforia.VuforiaInitError>,Vuforia.VuforiaInitError)
Vuforia.Internal.Core.Engine:add_OnAfterVuforiaInitializedPublic (System.Action`1<Vuforia.VuforiaInitError>)
Vuforia.VuforiaBehaviour:Awake ()

Someone can help me?

Thank you

The model target that is giving me this error I have tried by separately in a scene that alone and has not given me this error. Sorry for my English that is not very good, but I hope you understand my problem

You might get better traction with this question on the Vuforia forums: Getting Started | Vuforia Library