how can change active directory password

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ASP.NET

Hi,
I have a web page through this page when I try to add a new user then users created successfully but when try resetting their password then I am getting errors’
add New user successfully

public static void AddUser(ADUser adUser)
  {
      // Local variables
      DirectoryEntry oDE = null;
      DirectoryEntry oDENewUser = null;
      DirectoryEntries oDEs = null;
      try
      {
          oDE = GetDirectoryEntry(GetADPath(PROD, adUser.UserType));

          // 1. Create user account
          oDEs = oDE.Children;
          oDENewUser = oDEs.Add("CN=" + adUser.UserName, "user");

          // 2. Set properties
          SetProperty(oDENewUser, "givenName", adUser.FirstName);
          SetProperty(oDENewUser, "sn", adUser.LastName);
          SetProperty(oDENewUser, "mail", adUser.Email);
          SetProperty(oDENewUser, "sAMAccountName", adUser.UserName);
          oDENewUser.CommitChanges();
          /// 4. Enable account
          EnableAccount(oDENewUser);
          // 3. Set password
          //SetPassword(oDENewUser, adUser.Password);
          SetPassword1(oDENewUser.Path, adUser.Password);
          oDENewUser.CommitChanges();
          oDENewUser.Close();
          oDE.Close();
      }
      catch (Exception ex)
      {
          throw ex;
      }
  }

I have try the following 2 SetPassword methods but getting error.
Method 1.

internal static void SetPassword1(string path, string userPassword)
   {
       //Local variables
       DirectoryEntry usr = null;

       try
       {
           usr = new DirectoryEntry();
           usr.Path = path;
           usr.AuthenticationType = AuthenticationTypes.Secure;
           object ret = usr.Invoke("SetPassword", userPassword);
           usr.CommitChanges();
           usr.Close();
       }
       catch (Exception ex)
       {
           throw ex;
       }
   }

The exception raised (Error Code 80072035: The server is unwilling to process the request)
Method 2.

internal static void SetPassword(DirectoryEntry de, string userPassword)
        {
            //Local variables
            //DirectoryEntry usr = null;
            string quotePwd;
            byte[] pwdBin;
            
            try
            {
                quotePwd = String.Format(@"""{0}""", userPassword);
                pwdBin = System.Text.Encoding.Unicode.GetBytes(quotePwd);
                de.Properties["unicodePwd"].Value = pwdBin;
                de.CommitChanges();
                //usr.Close();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

The exception raised ("Exception has been thrown by the target of an invocation.")
Is there an easy way to tell if there is a problem with changing a password?
Please reply me as soon as possible.
Thanks.