I implemented uploadify 2.0.3 in my Drupal web site and it works perfectly in Firefox 3.0.14 and IE8 but with Chrome 2.0.172.43, Safari 4 and Opera 9, i always get a HTTP Error 403 at the end of each upload.
Working on localhost, Apache 2.2.11 with mod_rewrite enabled, Windows XP, PHP 5.2.9, Drupal 6.
Ok i managed to track the problem down, it somehow has to do with the PHP session object.
for those familiar with drupal, i removed the access permission of the menu item that maps the path to the function that is used to receive uploadify's uploads and it works fine now, this means that somehow the session is not well handled meaning that this is a bug rather than an implementation issue so i suggest this should be moved to the Bugs board.
This work around solves my issue but decreases security, hopefully the uploadify team will manage something out.