Changing Mysql functions to Mysqli breaks the script

I have this script that deletes a certain picture from the website. It's written with mysql functions so i wanted to update it to mysqli but doing so makes the script stop working. No die message from the script are shown no php errors and adding error_reporting(E_ALL); doesn't show any errors either.

Original script:

    if(isset($_POST['F3Verwijderen']))
    try 
    {                           
        //delete the file
        $sql = "SELECT PandFoto3 FROM tblpand WHERE `PK_Pand` = '".$pandid."'";

        $con = mysql_connect('WEBSITE.mysql', 'WEBSITE', 'PASS');
        if (!$con) {
        die('Could not connect: ' . mysql_error());
        }
        mysql_select_db("WEBSITE");
        $result = mysql_query($sql, $con);
        while ($row = mysql_fetch_array($result)) {                     
            if(file_exists($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3'])) {
                unlink($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3']);
            } else {
            echo $row['PandFoto3'];
            }
        }
        //delete the path url from the database field
        mysql_query("UPDATE tblpand SET PandFoto3 = NULL WHERE `PK_Pand` = '".$pandid."'");
        mysql_close($con);          


        header('Location: ../admin/pand-aanpassen.php?id='.$pandid);
    }

Updated to mysqli:

try 
    {                           
        //delete the file
        $sql = "SELECT PandFoto3 FROM tblpand WHERE `PK_Pand` = '".$pandid."'";

        $con = mysqli_connect('WEBSITE.mysql', 'WEBSITE', 'PASS');
        if (!$con) {
        die('Could not connect: ' . mysqli_error());
        }
        mysqli_select_db("WEBSITE");
        $result = mysqli_query($sql, $con);
        while ($row = mysqli_fetch_array($result)) {                        
            if(file_exists($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3'])) {
                unlink($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3']);
            } else {
            echo $row['PandFoto3'];
            }
        }
        //delete the path url from the database field
        mysqli_query("UPDATE tblpand SET PandFoto3 = NULL WHERE `PK_Pand` = '".$pandid."'");
        mysqli_close($con);         


        header('Location: ../admin/pand-aanpassen.php?id='.$pandid);
    }

via Chebli Mohamed