Interesting. The leading slashes seem to be the problem.
Changing the upload_url and file_destination_path are not going to change anything because those are all set in the BulkUploader_Controller when the field is instantiated.
Go to that section of the BulkUploader_Controller code (line 130-ish)
$fields = new FieldSet( new SWFUploadField("UploadForm","","",array( 'file_upload_limit' => '100', // how many files can be uploaded 'file_queue_limit' => '100', // how many files can be in the queue at once 'browse_button_text' => 'Choose files...', 'upload_url' => '/'.$this->RelativeLink('handleswfupload') )) );
try removing the leading slash on upload_url
Almost there! Thanks so much for all your testing.