If you are getting a "Invalid Descriptor Error" when trying to download your JAR, you should check the MIME types on your server. In fact, this should probably be the first thing you check. If the MIME type is incorrect then the handset won't even try to process the file.

Read all about MIME types in this post:
http://www.sprintdevelopers.com/modules.php?name=Forums&file=viewtopic&p...