Problem posting a form

<?php
//Create a new instance of the databaseAPI. Connect to our training DB.
$mydb= new DBAPI();
$mydb->connect($host='a host',$dbase='a db', $uid='a user',$pwd='a password');

//First off check if a discount code was posted by the user.
if (isset($_POST['discount_Code'])) {
  $search = $_POST['discount_Code'];
  $query_viewCode = "SELECT * FROM discount WHERE discount_Code = '$search'";
  $viewCode = $mydb->query($query_viewCode);
  $row_viewCode = mysql_fetch_assoc($viewCode);
  $totalRows_viewCode = mysql_num_rows($viewCode);
  //IF THE CODE WAS FOUND ALLOW THE DISCOUNT ELSE BOOT TO THE ERROR PAGE.
  if ($search != "") {
      if($totalRows_viewCode > 0) {
          $_SESSION['specialDiscountCode'] = $search;
      }else{
          $modx->sendRedirect("codeerror.html");	  
          exit; 
      }
  }
}

//Now we select the course to be booked.
if (isset($_POST["courses"])) {
  $courseprice = $_POST["courses"];
  $query_checkPrice = "SELECT course_Price FROM courses WHERE course_ID = $courseprice";
  $checkPrice = $mydb->query($query_checkPrice);
  $row_checkPrice = mysql_fetch_assoc($checkPrice);
  $totalRows_checkPrice = mysql_num_rows($checkPrice);

  $_SESSION['courseID'] = $_POST["courses"];
  $_SESSION['eventID'] = $_POST["dates"];
  $_SESSION['participantNumber'] = $_POST["participants"];
  $participants = $_SESSION['participantNumber'];
  $eventID = $_SESSION['eventID'];

  //Do a quick check for the total number of bookings for the selected event.
  //Count the number of bookings for the selected event
  $query_countEvent = "SELECT count(booking_ID) as eventCount FROM booking WHERE event_ID = '$eventID'";
  $countEvent = $mydb->query($query_countEvent);
  $row_eventCount = mysql_fetch_assoc($countEvent);
  $eventCount = $row_eventCount["eventCount"];
  //Now check event count againist the number of seats left
  $query_checkMax = "SELECT event_Max FROM event WHERE event_ID = '$eventID'";
  $checkMax = $mydb->query($query_checkMax);
  $row_checkMax = mysql_fetch_assoc($checkMax);
  $eventMax = $row_checkMax["event_Max"];
  //Now determine the amount of seats left on course
  $seatsLeft = $eventMax - $eventCount;
  //If the number of seats requested are not available, then re-diret the user to an error page
  if ($participants > $seatsLeft) {
      $modx->sendRedirect("coursefull.html");
  }
  $price = $row_checkPrice["course_Price"];
  $price = $price*$participants;
  //Get rid of the change or realex will explode.
  $price = round($price,0);
  $_SESSION['price'] = $price;

}else{
  //Because this page is dynamic we need to redirect to stop session errors for the back button is clicked.		 
  $modx->sendRedirect("booking.html");
}

//If they have got this far without a re-direct build up the form for them to enter details and output.

$i=1;
$out = 2;
$output = "";
		
while($i < $participants) {
  $output .= "<p><strong>Participant # $out </strong></p>";
  $output .= "<table border=\"0\" cellspacing=\"0\" cellpadding=\"0\"><tr><td width=\"27%\">First Name: *</td>";
  $output .= "<td width=\"70%\" height=\"30\"><input name=\"namep$i\" type=\"text\" id=\"namep$i\" size=\"22\">";
  $output .= "</td></tr><tr><td>Family Name: *</td><td height=\"30\"><input name=\"snamep$i\" type=\"text\" id=\"snamep\" size=\"22\">";     
  $output .= "</td></tr><tr><td>E-Mail address: *</td><td height=\"30\">";		  
  $output .= "<input name=\"emailp$i\" type=\"text\" id=\"emailp\" size=\"22\"></td></tr><tr>";
  $output .= "<td>Company:</td><td height=\"30\"><input name=\"companyp$i\" type=\"text\" id=\"companyp\" size=\"22\"></td></tr><tr>";      
  $output .= "<td>Postal Address: *</td><td height=\"30\"><input name=\"addressp$i\" type=\"text\" id=\"addressp\" size=\"22\"></td></tr><tr>";    
  $output .= "<td>Telephone: *</td><td height=\"30\"><input name=\"telephonep$i\" type=\"text\" id=\"telephonep\" size=\"22\"></td></tr><tr>";
  $output .= "<td>Mobile Phone:</td><td height=\"30\"><input name=\"mphonep$i\" type=\"text\" id=\"mphonep\" size=\"22\"></td></tr><tr>";
  $output .= "<td> </td><td> </td></tr></table><br>";
  $i++;
  $out++;
}

return $output;
?>