Variable has been assigned but has UnassignedReferenceExcecption

This is my script. You can see that declared some variables at top:

 var QuestAccepted = false;
 var TextBoxOnCheck: boolean = false;
 var MessageBox: GameObject;
 var TextBox: GameObject;
 var QuestBox: GameObject;
 var QuestText: GameObject;

 function OnMouseDown() {
     if(!TextBoxOnCheck) {
         MessageBox.SetActive(true);
 
         if(!QuestAccepted) {
             TextBox.GetComponent.<Text>().text = 'Villager: Hello, some bandit have stollen my money. Could you retrieve it from them on the other side of the river?\n[F] to Accept, [X] to refuse.';
         }
         else {
             TextBox.GetComponent.<Text>().text = 'Villager: Get going then!';
         }
     }
     else {
         MessageBox.SetActive(false);
     }
 
     TextBoxOnCheck = !TextBoxOnCheck;
 }
 
 function CloseMessageBox() {
     MessageBox.SetActive(false);
     TextBoxOnCheck = false;    
 }
 
 function AcceptQuest() {
     QuestText.GetComponent.<Text>().text = 'Active Quest: Recover the loot';
     QuestAccepted = true;
     TextBox.GetComponent.<Text>().text = 'Villager: Nice! I\'ll be waiting here, tell me when your job is done!';
 
     //yield WaitForSeconds(3);
     //CloseMessageBox();
 }
 
 function Update() {
     if(Input.GetButtonDown('Use')) {
         AcceptQuest();
     }
     else if(Input.GetButtonDown('Cancel')) {
         CloseMessageBox();
     }
 }

And those are assigned in inspector as I dragged and dropped. When the game starts, all functions works well but this error message is in the console:

 UnassignedReferenceException: The variable QuestText of Quest001 has not been assigned.
 You probably need to assign the QuestText variable of the Quest001 script in the inspector.
 UnityEngine.GameObject.GetComponent[Text] () (at C:/buildslave/unity/build/artifacts/generated/common/runtime/GameObjectBindings.gen.cs:38)
 Quest001.AcceptQuest () (at Assets/Scripts/Quest001.js:34)
 Quest001.Update () (at Assets/Scripts/Quest001.js:44)

I removed the script and re-attached but still won't worked. If it's actually didn't assigned, it should be not work but it is working. What am I missing?