Codeigniter Force download files

I've had similar problems. I think the problem resides in certain mime's and headers sent to the browser(s). I've end up using the code I found here http://taggedzi.com/articles/display/forcing-downloads-through-codeigniter. Use the function below instead of force_download. It has worked for me so far.

    function _push_file($path, $name)
    {
      // make sure it's a file before doing anything!
      if(is_file($path))
      {
        // required for IE
        if(ini_get('zlib.output_compression')) { ini_set('zlib.output_compression', 'Off'); }

        // get the file mime type using the file extension
        $this->load->helper('file');

        $mime = get_mime_by_extension($path);

        // Build the headers to push out the file properly.
        header('Pragma: public');     // required
        header('Expires: 0');         // no cache
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Last-Modified: '.gmdate ('D, d M Y H:i:s', filemtime ($path)).' GMT');
        header('Cache-Control: private',false);
        header('Content-Type: '.$mime);  // Add the mime type from Code igniter.
        header('Content-Disposition: attachment; filename="'.basename($name).'"');  // Add the file name
        header('Content-Transfer-Encoding: binary');
        header('Content-Length: '.filesize($path)); // provide file size
        header('Connection: close');
        readfile($path); // push it out
        exit();
    }
}

Hope it helps.

It is working for .pdfs also. Check the path to the file - that might be the problem.
I, too, had that problem, but when I corrected the path to the file, it worked perfectly.
The following is how I wrote the code:

if($src ==  "xyyx")
{
$pth    =   file_get_contents(base_url()."path/to/the/file.pdf");
$nme    =   "sample_file.pdf";
force_download($nme, $pth);     
}