function force_download($filename = '', $data = false, $enable_partial = true, $speedlimit = 0)
    {
        if ($filename == '')
        {
            return FALSE;
        }
        
        if($data === false && !file_exists($filename))
            return FALSE;

        // Try to determine if the filename includes a file extension.
        // We need it in order to set the MIME type
        if (FALSE === strpos($filename, '.'))
        {
            return FALSE;
        }
    
        // Grab the file extension
        $x = explode('.', $filename);
        $extension = end($x);

        // Load the mime types
        @include(APPPATH.'config/mimes'.EXT);
    
        // Set a default mime if we can't find it
        if ( ! isset($mimes[$extension]))
        {
            if (ereg('Opera(/| )([0-9].[0-9]{1,2})', $_SERVER['HTTP_USER_AGENT']))
                $UserBrowser = "Opera";
            elseif (ereg('MSIE ([0-9].[0-9]{1,2})', $_SERVER['HTTP_USER_AGENT']))
                $UserBrowser = "IE";
            else
                $UserBrowser = '';
            
            $mime = ($UserBrowser == 'IE' || $UserBrowser == 'Opera') ? 'application/octetstream' : 'application/octet-stream';
        }
        else
        {
            $mime = (is_array($mimes[$extension])) ? $mimes[$extension][0] : $mimes[$extension];
        }
        
        $size = $data === false ? filesize($filename) : strlen($data);
        
        if($data === false)
        {
            $info = pathinfo($filename);
            $name = $info['basename'];
        }
        else
        {
            $name = $filename;
        }
        
        // Clean data in cache if exists
        @ob_end_clean();
        
        // Check for partial download
        if(isset($_SERVER['HTTP_RANGE']) && $enable_partial)
        {
            list($a, $range) = explode("=", $_SERVER['HTTP_RANGE']);
            list($fbyte, $lbyte) = explode("-", $range);
            
            if(!$lbyte)
                $lbyte = $size - 1;
            
            $new_length = $lbyte - $fbyte;
            
            header("HTTP/1.1 206 Partial Content", true);
            header("Content-Length: $new_length", true);
            header("Content-Range: bytes $fbyte-$lbyte/$size", true);
        }
        else
        {
            header("Content-Length: " . $size);
        }
        
        // Common headers
        header('Content-Type: ' . $mime, true);
        header('Content-Disposition: attachment; filename="' . $name . '"', true);
        header("Expires: Mon, 26 Jul 1997 05:00:00 GMT", true);
        header('Accept-Ranges: bytes', true);
        header("Cache-control: private", true);
        header('Pragma: private', true);
        
        // Open file
        if($data === false) {
            $file = fopen($filename, 'r');
            
            if(!$file)
                return FALSE;
        }
        
        // Cut data for partial download
        if(isset($_SERVER['HTTP_RANGE']) && $enable_partial)
            if($data === false)
                fseek($file, $range);
            else
                $data = substr($data, $range);
        
        // Disable script time limit
        @set_time_limit(0);
        
        // Check for speed limit or file optimize
        if($speedlimit > 0 || $data === false)
        {
            if($data === false)
            {
                $chunksize = $speedlimit > 0 ? $speedlimit * 1024 : 512 * 1024;
            
                while(!feof($file) and (connection_status() == 0))
                {
                    $buffer = fread($file, $chunksize);
                    echo $buffer;
                    flush();
                    
                    if($speedlimit > 0)
                        sleep(1);
                }
                
                fclose($file);
            }
            else
            {
                $index = 0;
                $speedlimit *= 1024; //convert to kb
                
                while($index < $size and (connection_status() == 0))
                {
                    $left = $size - $index;
                    $buffersize = min($left, $speedlimit);
                    
                    $buffer = substr($data, $index, $buffersize);
                    $index += $buffersize;
                    
                    echo $buffer;
                    flush();
                    sleep(1);
                }
            }
        }
        else
        {
            echo $data;
        }
    }

http://codeigniter.com/forums/viewthread/71192/#351584

Force download function that worked well, Thanks.

Force download function

php

PHP