BCE0004: Ambiguous reference 'Quest': Quest, Quest.

I downloaded this from the assest store and when I imported it I got an error (the error is in the title) heres the script!

 @CustomEditor (Quest)
 class QuestEditor extends Editor 
 {
     var Manager : QuestManager;
     
     //Quest custom editor: makes creating quests easy and simple.
     function OnInspectorGUI () 
     {
         Manager = FindObjectOfType(QuestManager);
         EditorGUIUtility.LookLikeInspector();
         EditorGUIUtility.LookLikeControls();
         EditorGUILayout.Space();
         
         target.QuestCode = EditorGUILayout.TextField("Quest Code:", target.QuestCode);
         target.QuestOrder = EditorGUILayout.IntField("Quest Order:", target.QuestOrder);
         
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         
         target.QuestTitle = EditorGUILayout.TextField("Quest Title:", target.QuestTitle);
         EditorGUILayout.LabelField("Quest Objective (Short):");
         target.QuestObjective = EditorGUILayout.TextArea(target.QuestObjective, GUILayout.Height(30));
         EditorGUILayout.LabelField("Quest Description/Story (Long):"); 
         target.Description = EditorGUILayout.TextArea(target.Description, GUILayout.Height(80));
         target.UseScrollView = EditorGUILayout.Toggle("Use Scroll View:", target.UseScrollView);
         if(target.UseScrollView == true)
         {
             target.ScrollLength = EditorGUILayout.IntField("Scroll View Length", target.ScrollLength);
         }  
         target.ShowAfterFinished = EditorGUILayout.Toggle("Show When Completed:", target.ShowAfterFinished);
         if(target.ShowAfterFinished == true)
         {
             EditorGUILayout.LabelField("Completed Quest Message (Short):");
             target.FinishedQuestMessage = EditorGUILayout.TextArea(target.FinishedQuestMessage, GUILayout.Height(30));
         }    
         EditorGUILayout.LabelField("Speech Audio:");
         EditorGUIUtility.LookLikeInspector();
         target.Speech = EditorGUILayout.ObjectField(target.Speech, typeof(AudioClip)) as AudioClip;
         EditorGUIUtility.LookLikeControls();        
          
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         
         target.QuestGiverName = EditorGUILayout.TextField("Quest Giver Name:", target.QuestGiverName);
         EditorGUILayout.LabelField("Quest Giver Image:");
         EditorGUIUtility.LookLikeInspector();
         target.QuestGiverImage = EditorGUILayout.ObjectField(target.QuestGiverImage, typeof(Texture2D)) as Texture2D;
         EditorGUIUtility.LookLikeControls();
         
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         
          
         var Condition : SerializedProperty = serializedObject.FindProperty("Goal");
         Condition.arraySize = EditorGUILayout.IntField("Condition(s):", Condition.arraySize);
         serializedObject.ApplyModifiedProperties();
         if(Condition.arraySize < 1) Condition.arraySize = 1;
         
         if(Condition.arraySize >= 1)
         {
         
         for(var i : int = 0; i < Condition.arraySize; i++)
         {
             var x =  i + 1;
             EditorGUILayout.LabelField("Condition " + x.ToString() + ":");
             EditorGUILayout.LabelField("Condition Type:");
             target.Goal[i].Type = EditorGUILayout.EnumPopup(target.QuestTypes, target.Goal[i].Type);
             target.Goal[i].Message = EditorGUILayout.TextField("Condition Message: ", target.Goal[i].Message); 
             if(Manager.QuestStyle == 1)
             {
                 EditorGUILayout.LabelField("Objectif Icon:");
                 EditorGUIUtility.LookLikeInspector();
                 target.Goal[i].Icon = EditorGUILayout.ObjectField(target.Goal[i].Icon, typeof(Texture2D)) as Texture2D;
                 EditorGUIUtility.LookLikeControls(); 
             }
             if(target.Goal[i].Type == 0)
             {
                 target.Goal[i].Destination = EditorGUILayout.Vector3Field("Destination:",target.Goal[i].Destination);
                 target.Goal[i].TimeToStay = EditorGUILayout.FloatField("Time To Stay:",target.Goal[i].TimeToStay);
             } 
             else if(target.Goal[i].Type == 1 || target.Goal[i].Type == 3)
             {
                 target.Goal[i].ItemName = EditorGUILayout.TextField("Item/Target Name:", target.Goal[i].ItemName);
                 target.Goal[i].AmountRequired = EditorGUILayout.IntField("Amount:", target.Goal[i].AmountRequired);
             } 
             else if(target.Goal[i].Type == 2)
             {
                 EditorGUILayout.LabelField("Quest Giver To Meet:");
                 EditorGUIUtility.LookLikeInspector();
                 target.Goal[i].Target = EditorGUILayout.ObjectField(target.Goal[i].Target, typeof(Quest)) as Quest;
                 EditorGUIUtility.LookLikeControls();
                 EditorGUILayout.LabelField("Message On Arrival:");
                 target.Goal[i].ArrivalMessage = EditorGUILayout.TextArea(target.Goal[i].ArrivalMessage, GUILayout.Height(30));
             }   
         }
         
         }
 
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         EditorGUILayout.Space();
         
         target.ReturnToGiver = EditorGUILayout.Toggle("Return To Quest Giver:", target.ReturnToGiver);
         target.RewardPlayer = EditorGUILayout.Toggle("Reward Player:", target.RewardPlayer);
         if(target.RewardPlayer == true)
         {
             target.XP = EditorGUILayout.IntField("XP:", target.XP);
         }    
         EditorGUILayout.LabelField("Reward Item: Requires S-Inventory");
         EditorGUIUtility.LookLikeInspector();
         target.Item = EditorGUILayout.ObjectField(target.Item, typeof(GameObject)) as GameObject;
         EditorGUIUtility.LookLikeControls();
     }
 }