Product Download Upload Button Permission Denied

I have tried to upload downloadable products using the file upload button, but when I add new products in marketpress i get a forbidden message.

I have changed permission on wp-admin to 777, on media-upload.php to 777, even have wp-content 777, and uploads to 777. Seems to make no difference. The regular media uploader works fine, just not the uploader in marketpress.

You don't have permission to access /wp-admin/media-upload.php on this server.