error pops up when rendering table "DataTables warning" - php

Question

i have this code that will display the items perfectly but having a error pop up that i have to click "OK" too view the page
i have searched the web and from what i understand this has something to do with that the header table has more column than the data itself, i have tried to troubleshot this and got nowhere fast as i am a novice (noob) :/
if anyone can shed some light on this it would be great! :)
The Error
DataTables warning (table id = 'example'): Requested unknown parameter '0'
from the data source for row 0
My Code
<?php
//include database connection
include 'db_connect.php';
//query all records from the database
$query = "select * from repair_jobs";
//execute the query
$result = $mysqli->query( $query );
//get number of rows returned
$num_results = $result->num_rows;
//this will link us to our add.php to create new record
if( $num_results > 0){ //it means there's already a database record
//start table
//creating our table heading
echo "<table id='example' cellpadding='0' cellspacing='0' border='0' class='display' >";
echo "<thead><tr>";
echo "<th>Client</th>";
echo "<th>Type</th>";
echo "<th>Labour</th>";
echo "<th>ourcosts</th>";
echo "</thead></tr><tbody><tr class=\"gradeX\">";
//loop to show each records
while( $row = $result->fetch_assoc() ){
//extract row
//this will make $row['firstname'] to
//just $firstname only
extract($row);
//creating new table row per record
echo "<tr>";
echo "<td>{$client}</td>";
echo "<td>{$type}</td>";
echo "<td>{$labour}</td>";
echo "<td>{$ourcosts}</td>";
echo "</td>";
echo "</tr>";
}
echo "</table>";//end table
}else{
//if database table is empty
echo "No records found.";
}
//disconnect from database
$result->free();
$mysqli->close();
?>
it displays ok but this error puzzling me.