I've had a couple of web start programs on the web and they've been running fine. Couldn't see why the logs showed poor usage last month so I went in to check them and found they no longer run. I don't think I've changed anything and normally I test things quite fully before releasing (obviously were all human though). The two pages that have the issues are a javaarcade game and a java chess program. Other pages with applets on seem to run fine. The issues that show up are:
a) on the main web page next to the launch button it has some weird pop up saying "click here to activate the java deployment toolkit plugin". I have no idea what this is but it appears each time and looks ugly as hell. If I click it then the popup goes until next time I visit the page.
b) when I click the launch button it does the following:
Your jnlp does not have the main-class. Can you double check if your AlienSwarm.jar manifest file has it?
Another way of testing is download the AlienSwarm.jar to your local drive and double click it. If it is packaged correctly with all the required attributes, it should launch the application.