At least one of your JARs is not signed.
It's actually only one jar. I signed it on my dev PC and then transferred it to the server along with the jnlp file. I'll be the first to admit I'm feeling around in the dark here. I thought web start and jnlp were almost the same thing but obviously not - I'll google to find out more. Is it better to use JWS rather than JNLP then?
The downside is that people might get put off running the program if they're told it requires special permission to run. I think nothing of running any applet but I'm wary of running applications. Why it needs any permissions at all to just run in full screen mode and to access a web page (in the same directory) is beyond me (and perhaps this thread).
I believe a verified cert costs a few hundred $ which, for a free app, doesn't make sense.
JWS doesn't suffer from the same problem? JNLP files occasionally open with a text or xml editor.
I seem to get different behaviour depending on which PC I open the page on - my dev PC just goes quiet after loading the Java, my wife's PC just displays the XML on screen, none actually play the game which is a bit frustrating.
EDIT: actually when I run on my PC now it downloads the app, starts of Java, asks if it's OK to run and then says it's unable to run the application :
Name : Retro arcade game ...
Publisher : Mike Robinson
From file ://