You might have accidentally used the quotation marks (which should be omitted).
Using minor permutations, I found the following:
http://www.blackberryforums.com/show...d+.alx+convert
(Scroll down to see headtailgrep's post)
http://www.blackberryforums.com/show....jar+mimetypes
(Config info, if you want to use webserver method)
Hope this helps.