Make sure the JNLP file is not cached. I.e., each time you try something new, have you renamed / relocated the JNLP file?
Regarding your updates,
The only ting that comes to my mind is that you need to make sure that your script responds with the correct mime type: application/x-java-jnlp-file
That is, from your cgi-script, you have to provide the HTTP header field
Content-Type: application/x-java-jnlp-file
aioobe
2010-10-29 07:55:03