I am guessing that your path to the swf
or image
assets are wrong.
From the github page:
swf: ‘media/downloadify.swf’ Required
Path to the SWF File. Can be relative from the page, or an absolute path.
downloadImage: ‘images/download.png’ Required
Path to the Button Image. Can be relative from the page or an absolute path.
Your example exactly copies the working example for those paths.
yours:
media/downloadify.swf
queue_name=downloadify_1361560979222&width=100&height=30&downloadImage=images/download.png
Theirs:
media/downloadify.swf
queue_name=downloadify_1361561050132&width=100&height=30&downloadImage=images/download.png
I am betting that those assets are not located in the same place on your server. Otherwise your download object is there and should be working.