警告：mysqli_fetch_row（）期望参数1为mysqli_result

I am sorry I ask questions, I am fairly new with php and mysql, i am fairly new to understanding debugging. I created this adding member/friend file and the process file has an error

Warning: mysqli_fetch_row() expects parameter 1 to be mysqli_result, boolean given in line 57  

which is the $countArr = mysqli_fetch_row($countResult2);

I've also received this error

Warning: Cannot modify header information - headers already sent by 

which is the header:location part, ive search how to fix this, but I do not understand how to implement the ob_start(); code if this is the correct way to fix it.

Anybody know why it is like that? if so, could you kindly explain it. Thank you so much

below is the code, called memberaddprocess.php

 <?php
//////////////////////////////////////
    session_start();
    require_once('sqlconnect.inc.php');
/////////////////////////////////////

    $memberHid1 = $_POST['memberHid1'];  
    $new_session = $_POST['memberHid']; 
//connecting to the database
$conn = @mysqli_connect($host, 
        $user, 
        $pswd, 
        $dbnm);

    if (!$conn) {
        echo "<p>Database connection failure</p>"; 
    } else {

    @mysqli_select_db($conn, $dbnm)
        or die ("Database not available");
    }

    $query = "SELECT member_id 
              FROM team 
              WHERE member_name = '$memberHid1'";

    $queryResult = @mysqli_query($conn, $query)
                or die ("<p>Unable to execute query.</p>". "<p>Error code:" . mysqli_errno($conn) .":" . mysqli_error($conn));

    $fetchArr = mysqli_fetch_row($queryResult);

    $memberHid3 = $fetchArr[0];             
    $memberHid = $_SESSION['membername'] = $new_session;

    $query2 = "SELECT member_id 
               FROM team 
               WHERE member_name = '$memberHid'";

    $queryResult2 = @mysqli_query($conn,$query2)
        or die ("<p>Unable to execute query.</p>". "<p>Error code" . mysqli_errno($conn) .":" . mysqli_error($conn));

    $fetchArr2 = mysqli_fetch_row($queryResult2);
    $memberHid4 = $fetchArr2[0];

    $query3 = "INSERT INTO myteam 
               VALUES($memberHid4, $memberHid3)";

    $queryResult3 = @mysqli_query($conn,$query3)
        or die ("<p>Unable to execute query.</p>". "<p>Error code" . mysqli_errno($conn) .":" . mysqli_error($conn))."</p>";
                echo "<p>$memberHid1"."  "." Successfully added</p>";

        $queryCount = "SELECT COUNT(*) 
                       FROM team";
        $countResult = @mysqli_query($conn,$queryCount);
        $fetchCountArr = mysqli_fetch_row($countResult);    
        for($n=0;$n<$fetchCountArr[0];$n++)
        {
            $pst = $n+1;
            $query4 = "SELECT member_id2
                        FROM myteam 
                        WHERE friend_id1 = '$pst'";

            $countResult2 = @mysqli_query($conn,$query4);
            $countArr = mysqli_fetch_row($countResult2);
            $a=0;
            while($countArr)
            {
                $a++;
                $countArr = mysqli_fetch_row($countResult2); //echo "<p>$a</p>";
            }

            $query4 = "UPDATE team 
                       SET num_of_members= '$a' 
                       WHERE member_id = '$pst'";

            $countResult2 = @mysqli_query($conn,$query4);

        }

    $querySelect = "SELECT member_id2 
                    FROM myteam 
                    WHERE member_id1 = '$memberHid4'";

    $querySelectResult = @mysqli_query($conn, $querySelect);
    $fetchArr = mysqli_fetch_row($querySelectResult);

    while($fetchArr)
    {
        foreach($fetchArr as $value)

        {
            //echo $value;
            $querySelect2 = "SELECT member_name 
                            FROM friends where friend_id='$value'";
            $querySelectResult2 = @mysqli_query($conn, $querySelectResult2);
            $fetchArr2 = mysqli_fetch_row($querySelectResult2);
            foreach($fetchArr2 as $value)
            {
                //echo $value;
            }       
        }
        $fetchArr = mysqli_fetch_row($querySelectResult);
    }

     header('Location: memberadd.php'); //redirecting to home page
     exit();

?>

i think this will help you

 <?php 
          $query4 = "SELECT member_id2
                    FROM myteam 
                    WHERE friend_id1 = '$pst'";

        $countResult2 = @mysql_query($query4,$conn);
        $countArr = mysql_fetch_array($countResult2);
        echo $countArr['member_id2'];
    ?>