I am creating a checkers game but My miniMax is not functioning properly,it is always switching between two positions for its move(index 20 and 17).Here is my code:

 public double MiniMax(int[] board, int depth, int turn, int red_best, int black_best)

{

  int source;
  int dest;
  double MAX_SCORE=-INFINITY,newScore;
  int MAX_DEPTH=3;
  int[] newBoard=new int[32];
  generateMoves(board,turn);
  System.arraycopy(board, 0, newBoard, 0, 32);
  if(depth==MAX_DEPTH)
  { return Evaluation(turn,board);}
  for(int z=0;z<possibleMoves.size();z+=2){
        source=Integer.parseInt(possibleMoves.elementAt(z).toString());
        System.out.println("SOURCE= "+source);

        dest=Integer.parseInt(possibleMoves.elementAt(z+1).toString());//(int[])possibleMoves.elementAt(z+1);
        System.out.println("DEST = "+dest);
        applyMove(newBoard,source,dest);
        newScore=MiniMax(newBoard,depth+1,opponent(turn),red_best, black_best);
        if(newScore>MAX_SCORE)
        {MAX_SCORE=newScore;maxSource=source; maxDest=dest;}//maxSource and maxDest will be used to perform the move.

        if (MAX_SCORE > black_best) 
        {
            if (MAX_SCORE >= red_best) 
                break;  /*  alpha_beta cutoff  */
            else
                black_best = (int) MAX_SCORE;  //the_score
        }
        if (MAX_SCORE < red_best) 
        {
            if (MAX_SCORE<= black_best) 
                break;  /*  alpha_beta cutoff  */
            else
                red_best = (int) MAX_SCORE;  //the_score
        }

  }//for ends


  return MAX_SCORE;

} //end minimax

I am unable to find out the logical mistake. Any idea what's going wrong?