Error interpreting jpeg image when downloading

The error is as follows:

"(Error interpreting JPEG image file (Not a JPEG file: starts with 0x3c 0x70)"

And this is my script to download files:

//Extensión del archivo para elegir el mime type
switch ($ext) {
case 'pdf':
  $headerType = 'application/pdf';
  break;
case 'png':
  $headerType = 'image/png';
  break;
case 'jpg':
  $headerType = 'image/jpg';
  break;
case 'jpeg':
  $headerType = 'image/jpeg';
  break;
case 'gif':
  $headerType = 'image/gif';
  break;
case 'xls':
  $headerType = 'application/excel';
  break;
case 'doc':
  $headerType = 'application/msword';
  break;
default:
  $headerType = 'application/octet-stream';
  break;
}

header('Content-type: '.$headerType.'');

$fp = fopen("php://output", "w");
ftp_fget($conn_id,$fp,$value,FTP_BINARY, 0);

On my server if I can open it well, but when downloading it through the system, does this error occur to me, is it an error with mimeType or is it something else?