Gotta love www.php.net! I'll get an update together within the next couple of days. In the interim, you'll need to edit /YOUR_ADMIN/add_customers_backend.php, adding one line and changing another around line 40:
Code:
...
function check_file_upload() {
  global $db, $row_positions, $post, $acfa_lines;

  $files = $_FILES['bulk_upload'];
  $errors = array();
  $to_insert = array();

  if (!zen_not_null($files['name'])) {
    $errors[] = ERROR_NO_UPLOAD_FILE;
  
  } else {
    if ($files['error'] != 0) {
    $errors[] = sprintf (ERROR_FILE_UPLOAD, $files['error']);
    
    } else {
      $pos = strrpos($files['name'],'.')+1;
      $allowed_extensions = array ( 'TXT', 'CSV' );
      $extension = substr ($files['name'], $pos);
      if ( (strlen ($extension) < 1 ) || !in_array(strtoupper($extension), $allowed_extensions) ) {
      $errors[] = sprintf (ERROR_BAD_FILE_EXTENSION, $extension) . implode(', ', $allowed_extensions);
    
      } else {
        $path = DIR_FS_UPLOADS . $files['name'];

        if (!move_uploaded_file($files['tmp_name'], $path)) {
          $errors[] = ERROR_CANT_MOVE_FILE;
      
        } else {
          chmod($path, 0775);
          ini_set("auto_detect_line_endings", true);  /*v2.0.3a*/
          $lines = file($path, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);  /*v2.0.3c*/

...
I'll also beef up some of the error-detection that's present in the files ...