Your code was missing some curly brackets ( {} ):
include ("../dbconnect.php");
$sql="SELECT c.endofmonthform, c.startofmonthform, c.email, c.id, c.formlevel, c.mastersite, c.opmanager, u.userEmail FROM `clients` as c LEFT JOIN `users` as u on c.opmanager = u.userName WHERE endofmonthform="22/09/2016""; //TODAYS DATE BACK HERE!
$result=mysql_query($sql); 
 while($row=mysql_fetch_array($result)){  
    $enddate = $row['endofmonthform']; // End
    $startdate = $row['startofmonthform']; // Start
    $email = $row['email']; //Email to send email to
    $id = $row['id'];
    $formlevel = $row['formlevel']; //To update and check formlevel
    $sitegroupname = $row['mastersite'];
    $manager = $row['opmanager'];
    $opemail = $row['userEmail'];
    /* If end date is today and form level is still ZERO then send email to op manager */
    $mail = new EMail;
    $mail->Username="Sender email";    
    $mail->Password = 'mypwd';
    $mail->SetFrom("[email protected]","companyname");  
    $mail->ContentType = "text/html";
    $mail->Subject = "Client feedback incomplete NEW LAYOUT";
    //Enter the email address you wish to send TO (Name is an optional friendly name):
    $mail->AddTo($opemail,$manager);
    $mail->Message = "<!DOCTYPE html PUBLIC  -//W3C//DTD XHTML 1.0 Transitional//EN   http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd >
    <html xmlns=http://www.w3.org/1999/xhtml>
    <head>
    <meta http-equiv=Content-Type  content=text/html; charset=utf-8 />
    <title></title>
    <style type=text/css >
    body {margin: 0; padding: 0; min-width: 100%!important;}
    .content {width: 100%; max-width: 600px;}  
    </style>
    </head>
    <body yahoo bgcolor=#f6f8f1 >
    <table width=100% bgcolor=#f6f8f1 border=0 cellpadding=0 cellspacing=0>
    <tr>
    <td>
    <table class=content  align=center  cellpadding=0  cellspacing=0  border=0 >
    <tr>
    <td>
    ID: ".$id." <br>
    Clients group name: ".$sitegroupname." <br>
    Managers Name: ".$manager." <br>
    Managers Email: ".$useremail." <br>
    Please log into your account as you have feedback notifications
    <br>
    </td>
    </tr>
    </table>
    </td>
    </tr>
    </table>
    </body>
    </html>";
    echo $success = $mail->Send(); //Send the email.
}
Also cleaned up some of the PHP to simplify the entire thing.
NOTE: I excluded the email class as it isn’t relevant to this problem.
EDIT:
TS informed me that the mail part wasn’t working, so try using the default php mailer:
<?php 
include ("../dbconnect.php");
$sql="SELECT c.endofmonthform, c.startofmonthform, c.email, c.id, c.formlevel, c.mastersite, c.opmanager, u.userEmail FROM `clients` as c LEFT JOIN `users` as u on c.opmanager = u.userName WHERE endofmonthform="22/09/2016""; //TODAYS DATE BACK HERE!
$result=mysql_query($sql); 
 while($row=mysql_fetch_array($result)){  
    $enddate = $row['endofmonthform']; // End
    $startdate = $row['startofmonthform']; // Start
    $email = $row['email']; //Email to send email to
    $id = $row['id'];
    $formlevel = $row['formlevel']; //To update and check formlevel
    $sitegroupname = $row['mastersite'];
    $manager = $row['opmanager'];
    $opemail = $row['userEmail'];
    mail($opemail, "subject", "message", "from");
}
2
solved PHP send email foreach user