Need assistance with "Warning: Cannot modify header information - headers already sent by..."

This script prints all of the data correctly, however, I am getting the following error:
"Warning: Cannot modify header information - headers already sent by"

How do I fix?  What is the trick??

/***** EDIT BELOW LINES *****/
$DB_Server = "localhost"; // MySQL Server
$DB_Username = "username"; // MySQL Username
$DB_Password = "password"; // MySQL Password
$DB_DBName = "database"; // MySQL Database Name
$DB_TBLName = "backorders"; // MySQL Table Name
$xls_filename = 'BD_backorders_'.date('m-d-Y').'.xls'; // Define Excel (.xls) file name
// Create MySQL connection
$sql = "Select * from $DB_TBLName";
$Connect = @mysql_connect($DB_Server, $DB_Username, $DB_Password) or die("Failed to connect to MySQL:<br />" . mysql_error() . "<br />" . mysql_errno());
// Select database
$Db = @mysql_select_db($DB_DBName, $Connect) or die("Failed to select database:<br />" . mysql_error(). "<br />" . mysql_errno());
// Execute query
$result = @mysql_query($sql,$Connect) or die("Failed to execute query:<br />" . mysql_error(). "<br />" . mysql_errno());
// Header info settings   //ERROR HERE IN THIS SECTION ***************************
header("Content-Type: application/xls");
header("Content-Disposition: attachment; filename=$xls_filename");
header("Pragma: no-cache");
header("Expires: 0");
/***** Start of Formatting for Excel *****/
// Define separator (defines columns in excel &amp; tabs in word)
$sep = "\t"; // tabbed character
// Start of printing column names as names of MySQL fields
for ($i = 0; $i<mysql_num_fields($result); $i++) {
  echo mysql_field_name($result, $i) . "\t";
// End of printing column names
// Start while loop to get data
while($row = mysql_fetch_row($result))
  $schema_insert = "";
  for($j=0; $j<mysql_num_fields($result); $j++)
    if(!isset($row[$j])) {
      $schema_insert .= "NULL".$sep;
    elseif ($row[$j] != "") {
      $schema_insert .= "$row[$j]".$sep;
    else {
      $schema_insert .= "".$sep;
  $schema_insert = str_replace($sep."$", "", $schema_insert);
  $schema_insert = preg_replace("/\r\n|\n\r|\n|\r/", " ", $schema_insert);
  $schema_insert .= "\t";
  print "\n";

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lawrence_devAuthor Commented:
Thanks Gr8Gonzo, that is exactly what it was!!   Really appreciate you showing me instead of just throwing a 'link' out there!
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