Program stopped working

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 java arcade 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:

downloads the jnlp

scans for virus

runs java 7

downloads the app

say unable to launch

The details are as follows:

<jnlp spec="1.0+" codebase="http://www.checkmypages.com/swarm/" href="AlienSwarm.jnlp">
  <information>
    <title>Alien Swarm - retro arcade game</title>
    <vendor>Mike Robinson</vendor>
    <description>Alien Swarm</description>
    <icon href="example.png" kind="splash"/>
    <icon href="AlienSwarm.ico" kind="default"/>
    <offline-allowed/>
    <shortcut online="false">
      <desktop/>
    </shortcut>
  </information>
  <security>
    <all-permissions/>
  </security>
  <resources>
    <j2se version="1.4+"/>
    <jar href="AlienSwarm.jar"/>
  </resources>
  <application-desc/>
</jnlp>

java.lang.NullPointerException
	at java.util.zip.ZipFile.<init>(Unknown Source)
	at java.util.zip.ZipFile.<init>(Unknown Source)
	at java.util.jar.JarFile.<init>(Unknown Source)
	at java.util.jar.JarFile.<init>(Unknown Source)
	at com.sun.javaws.LaunchDownload.getMainClassName(Unknown Source)
	at com.sun.javaws.Launcher.doLaunchApp(Unknown Source)
	at com.sun.javaws.Launcher.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

Any ideas where I should look?

Mike

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.