OnTriggerExit Bugs <Internal error: Too many pairs created, new pairs will be ignore>

When the game start, a piece of road will translating and when it is OnTriggerExit from a collider(Used for detection), it will randomly generate a new straight road, or bended road, to continue the path of previous one.

The problem is, sometime when I click play button in Unity3D to start the game, after the OnTriggerExit is triggered, the system will suddenly generate a lot of the roads from resources folder, resulting <Internal error: Too many pairs created, new pairs will be ignored. This is perhaps due to an excessive number of objects created at one location.: >, but sometimes it won't encounter this problem. Is this a bug of the Unity3d? Please help. Thank you.

PHP:

function OnTriggerExit(collider : Collider){

  if(collider.gameObject.tag == "RoadObject" || collider.gameObject.tag == "RoadObject_Bend")
      CalculateNextTurnRoad();
}

function CalculateNextTurnRoad(){

   _roadType = Random.Range(0, 2);

   if(_roadType == 1)
      GenerateRoad(1);

   else
      GenerateRoad(0);


} 

function GenerateRoad(roadType:int){

   //Instantiating new GameObject from Resources Folder.

}


 

Problem Solved. 3D Mesh is not in good shape, resulting flaws in Mesh Collider. Therefore, I put a Box Collider for the road model instead of using Mesh Collider. Hope this will help others who encounter this problem in future.