SWFUpload image upload fails on PHP with 'Partial File Uploaded'

Okay, so this is a tough one, I've spent hours looking for a solution/problem. I'm using SWFUpload to upload images without reloading the page (with a fancy progressbar too), this works fine when I'm on localhost (Wamp server), but it goes nuts when I try to do so on my real linux server (which is the only possible flag as far as I could see), it's running Apache2 and PHP5. As I said the front-end is fine (apart maybe from the fact it's flash). The back-end code is as follows:

SWFUpload_settings.js

var swfu_settings ={upload_url  : "upload.php",
                flash_url   : "flash/swfupload.swf",
                button_placeholder_id   : "upload_flash",
                file_size_limit : "2 MB",
                file_types  : "*.gif;*.jpg;*.png",
                file_post_name  :   "Filedata",
                file_queue_limit    :   1,
                post_params     :   {
                        "PHPSESSID" : getCookie()
                },
                upload_start_handler    : upload_start,
                upload_error_handler    : upload_error,
                upload_complete_handler : upload_complete,
                upload_progress_handler : upload_progress,
                file_queued_handler :   file_queued,
                button_disabled : false,
                button_width : 120, 
                button_height : 22,
                button_text : '<div class="adm_upload">Select image</div>',
                button_text_style : '.adm_upload{color:#ff0000;}'
                };

upload.php

function manageUpload(){
        if( isset($_FILES['Filedata']) ){
            $dest_dir = $_SERVER[DOCUMENT_ROOT]."/images/products";
            $destination =  $_SERVER[DOCUMENT_ROOT]."/images/products/" . $_FILES['Filedata']['name'];
            if( is_dir($dest_dir) ){
                if( is_writable($dest_dir) ){
                    if( !move_uploaded_file($_FILES['Filedata']['tmp_name'], $destination ) ){
                        $html_body = '<h1>File upload error!</h1>';
                        switch ($_FILES['Filedata']['error']) {
                            case 1:
                                $html_body .= 'The file is bigger than this PHP installation allows';
                                break;
                            case 2:
                                $html_body .= 'The file is bigger than this form allows';
                                break;
                            case 3:
                                $html_body .= 'Only part of the file was uploaded';
                                break;
                            case 4:
                                $html_body .= 'No file was uploaded';
                                break;
                            default:
                                $html_body .= 'unknown errror';
                        } 
                        echo ($html_body);
                    }
                }
                else{
                    echo "Says it's not writable: ".$dest_dir;
                }
            }
            else{//not a directory?
                echo "Says it's not a directory:".$dest_dir;
            }
        }
        else{
            echo "No file POSTED.\n";
        }
    }

The only error that I get is from $_FILES['Filedata']['error'] = 3, 'Only part of the file was uploaded'. The destination directory does have 777 permission and you can see I made the required checks. It simply will not work, I have no idea why. Also, the files I tried uploading had no spaces in the filename, so that shouldn't fit under the issue 206 with SWFUpload.

As far as I can tell it can be either due to the front-end SWFUpload or back-end server configuration. Please help.

P.S. no need to mention security, this is only allowed to be used by the server admin with external access anyhow, plus there's the front-end limitation on the files he can select (images). There was no point securing it further.

Solution

So it turns out the problem was with the SWFUpload itself, it simply failed when used with linux servers. To anyone who has similar problems, consider using this instead:

ridiculously easy to adapt, works out of the box and you can customize it to your hearts content with ease. I implemented all I wanted in under 20 minutes, it's a pure delight to use and works well. Beautifully designed.