NullReferenceException: Object reference not set to an instance of an object

Hi, I am pretty new to C# and unity at the start, I downloaded complete project from unity asset store and import in unity5.3, but I am getting error as follows. However it has bugged me for so long, that I couldn't get it over even after I research it over the internet.

NullReferenceException: Object reference not set to an instance of an object UNIPlayerManagerCOMSelection.Update () (at Assets/3rd Lib/OpenNI/Scripts/User Selector/Selectors/UNIPlayerManagerCOMSelection.cs:18)

Codes as bellow

using UnityEngine; using System.Collections;

public class UNIPlayerManagerCOMSelection : UNIPlayerManager { public float m_maxAllowedDistance = 100000.0f;//defines a maximum distance, we can't have depth farther than this. public float m_failurePenalty = 10000.0f;//Defines the penalty (in mm) for users who failed to track and have not moved. public float m_minCOMChangeForFailure = 200.0f;//The minimum change in COM needed to retry a failure public float m_hysteresis = 100;//Holds the hysteresis used.

 protected override UNIPlayerCandidateObject GetNewUserObject (int userID)
 {
     return new UNIPlayerCOMCandidateObject(m_settingManager,userID);
 }
 
 public void Update()
 {
     foreach(UNIPlayerCandidateObject user in m_users)
     {
         UpdateUserPriority(user);
     }
     
     for(int i=0;i<m_users.Count ;i++)
     {
         UNIPlayerCOMCandidateObject bestUser = m_users[i] as UNIPlayerCOMCandidateObject;
         int bestIndex =i;
         for(int j = i+1;j<m_users.Count;j++)
         {
             UNIPlayerCOMCandidateObject curUser = m_users[j] as UNIPlayerCOMCandidateObject;
             if(curUser.m_priority > bestUser.m_priority)
             {
                 bestUser = curUser;
                 bestIndex = j;
             }
         }
         if(bestIndex !=i)
         {
             m_users[bestIndex] = m_users[i];
             m_users[i]= bestUser;
         }
     }
     int numUsersToPlayers = Mathf.Min (m_players.Count,m_users.Count);//the actual number of users which are players
     
     // first we will unselect all irrelevant players
     for(int i=numUsersToPlayers;i<m_users.Count;i++)
     {
         int playerNum = GetPlayerIdFromUser(m_users[i]);
         UnselectPlayer(playerNum);
     }
     //now we just have selected players so we need to select the good ones and put them in empty places
     
     for(int i=0;i<numUsersToPlayers;i++)
     {
         int playerNum = GetPlayerIdFromUser(m_users[i]);
         if(playerNum>=0)
             continue;//it is already selected
         
         for(int j = 0;j<m_players.Count ;j++)
         {
             if(m_players[j].Valid == false)
             {
                 m_players[j].User = m_users[i];
                 m_players[j].User.SelectUser(m_numRetries);
                 break;
             }
         }
     }
 }
 
 public override string GetSelectionString ()
 {
     return "User selector based on closet user";
 }
 
 
 protected void UpdateUserPriority(UNIPlayerCandidateObject user)
 {
     UNIPlayerCOMCandidateObject userCOM = user as UNIPlayerCOMCandidateObject ;
     if(userCOM == null)
         return; //irrelevant
     
     Vector3 com = m_settingManager.UserGenerator.GetUserCenterOfMass(userCOM.OpenNIUserID);
     userCOM.m_priority = com.z;
     if(userCOM.m_priority >0)
     {
         userCOM.m_priority =-m_maxAllowedDistance ;//as far away as possible for an illegal value
     }
     if(user.PlayerStatus == UserStatus.Selected || user.PlayerStatus == UserStatus.Tracking)
     {
         userCOM.m_priority += m_hysteresis;
     }
     if(userCOM.PlayerStatus == UserStatus.Failure)
     {
         com -= userCOM.m_COMPosWhenFail;
         if(com.magnitude < m_minCOMChangeForFailure)
         {
             userCOM.m_priority -= m_failurePenalty;
         }
     }
 }

}