Can't upload 5mb file using AJAX file uploader

I am using the file uploader plugin (from: https://github.com/valums/file-uploader) to upload files to my website.

If you are using a moden web browser (like Firefox 6 or Chrome 13), then it uploads by streaming the file in the POST body, and can give you a progress bar. If you're using IE (or an old browser), it falls back on the standard $_FILES (using a hidden iFrame).

Everything was working fine, but suddenly I can't upload 5MB files in Chrome or Firefox. When I upload a 5MB file in Chome or Firefox I get a 500 error and my PHP code is never even ran. If I use Internet Explorer (which uses $_FILES), it works fine.

This has to be a configuration problem, as my PHP code never even runs. So, I checked my settings.

/etc/php.ini

upload_max_filesize = 15M
post_max_size = 16M

I looked for LimitRequestBody, but that's nowhere to be found (and the default is unlimited).

Settings look right. I debugged this for a while, and I can not figure out what is wrong.

Is there a setting I'm missing? The server has suhosin installed, if that matters.

Here is the backend (I'm using CodeIgniter) code I'm using.

// Can we use the fancy file uploader?
if($this->input->get('qqfile') !== FALSE){ // Yes we can :-)
    $name = preg_replace('/[^\-\(\)\d\w\.]/','_', $this->input->get('qqfile'));
    // Upload the file using black magic :-)
    $input = fopen("php://input", 'r');
    $temp = tmpfile();
    $fileSize = stream_copy_to_stream($input, $temp);
    fclose($input);
    if($fileSize > 15728640){
        $ret['error'] = 'File not uploaded: file cannot be larger than 15 MB';
    }               
    elseif(isset($_SERVER['CONTENT_LENGTH']) && $fileSize === (int)$_SERVER['CONTENT_LENGTH']){
        $path = $folder.'/'.$name; // Where to put the file
        // Put the temp uploaded file into the correct spot
        $target = fopen($path, 'w');
        fseek($temp, 0, SEEK_SET);
        stream_copy_to_stream($temp, $target);
        fclose($target);
        fclose($temp);

        $ret['fileSize'] = $fileSize;
        $ret['success'] = true;
    }
    else{
        $ret['error'] = 'File not uploaded: content length error';
    }
}
else{ // IE 6-8 can't use the fancy uploader, so use the standard $_FILES
    $file = $_FILES['qqfile'];
    $file['name'] = preg_replace('/[^\-\(\)\d\w\.]/','_', $file['name']);
    $config['file_name'] = $file['name'];
    // Upload the file using CodeIgniter's upload class (using $_FILES)
    $_FILES['userfile'] = $_FILES['qqfile'];
    unset($_FILES['qqfile']);
    $config['upload_path'] = $folder;
    $config['allowed_types'] = '*';
    $config['max_size'] = 15360; //15 MB
    $this->load->library('upload', $config);
    if($this->upload->do_upload()){ // Upload was successful :-)
        $upload = $this->upload->data();
        $ret['success'] = true;
        $ret['fileSize'] = $upload['fileSize']/1000;
    }
    else{ // Upload was NOT successful
        $ret['error'] = 'File not uploaded: '.$this->upload->display_errors('', '');
        $ret['type'] = $_FILES['userfile']['type'];
    }
    echo json_encode($ret);
}

I know my code works, as files less than 4MB upload fine (on all browsers). I only have a problem with files bigger than 5mb (using Chrome/Firefox). The weird thing is, this works fine on my test server, but not my production server. They probably have different settings (suhosin is on production, but not on test).

Please check whether your php.ini settings are correctly loaded by viewing <?php phpinfo(); ?>.

I looked in my apache logs, and found