Java SE (Java Platform, Standard Edition)

Dear all
We are currently developing a simulation based educational game for schools. For most users, the download and starting of the game using java web start goes without any problem. However,
one user reports the following problem:

com.sun.deploy.net.JARSigningException: Found unsigned entry in resource: http://www.pidstop.com:80/energispillet_v2_2/webstart/jar/code_energy_signed.jar
                at com.sun.javaws.security.SigningInfo.getCommonCodeSignersForJar(Unknown Source)
                at com.sun.javaws.security.SigningInfo.check(Unknown Source)
                at com.sun.javaws.LaunchDownload.checkSignedResourcesHelper(Unknown Source)
                at com.sun.javaws.LaunchDownload.checkSignedResources(Unknown Source)
                at com.sun.javaws.Launcher.prepareLaunchFile(Unknown Source)
                at com.sun.javaws.Launcher.prepareToLaunch(Unknown Source)
                at com.sun.javaws.Launcher.prepareToLaunch(Unknown Source)
                at com.sun.javaws.Launcher.launch(Unknown Source)
                at com.sun.javaws.Main.launchApp(Unknown Source)
                at com.sun.javaws.Main.continueInSecureThread(Unknown Source)
                at com.sun.javaws.Main$1.run(Unknown Source)
                at java.lang.Thread.run(Unknown Source)

The user is running Java 1.6.0_17 on a pc with Windows 7.

It should also be mentioned that the same game runs without any problem on several hundred PCs.

The game is available from [http://www.energispillet.no/] (click on the screenshot) (Sorry, but the game is currently only in Norwegian...)
The direct link to the jnlp-file: [http://www.energispillet.no/energispillet_v2_2u3.jnlp]

The jnlp-file is as follows:

<?xml version="1.0" encoding="utf-8"?>

<!-- JNLP file for the energy game -->
<jnlp codebase="http://www.pidstop.com:80/energispillet_v2_2/" href="energispillet_v2_2u3.jnlp">
	<information>
		<!-- Description etc. of the file -->
		<title>Energispillet</title>
		<vendor>Cyberlab</vendor>
		<homepage href="http://www.energispillet.no"/>
		<description>Energispillet</description>
		<description kind="short">Energispillet v2.2</description>
		
		<!-- Icons -->
		<icon href="webstart/jar/energy_icon.png"/>
		<icon kind="splash" href="webstart/jar/energy_logo_text.png"/>
		
		<!-- Allow offline use -->
		<offline-allowed/>
		
		<!-- 
			Give Java Web Start hints that it could place shortcut on desktop and start menu.
			Does not guarantee that it will actually happen - but it works on some systems.
		-->
		<shortcut online="false">
		  <desktop/>
		  <menu submenu="Energispillet"/>
		</shortcut>
	</information>
	
	<resources>
		<!-- Path to jar file, relative to jnlp codebase -->
		<jar href="webstart/jar/code_energy_signed.jar" />
		<jar href="webstart/jar/code_energy_xml_signed.jar" />
		<jar href="webstart/jar/code_pidstop_signed.jar" />
		<jar href="webstart/jar/images_signed.jar" />
		
		<!--
			This will ensure jave version 1.6+ and 128MB initial and 256MB max memory.
			It will also provide java auto-download for users with older versions of java.
		-->
		<j2se version="1.6+" java-vm-args="-Xms128m -Xmx256m" href="http://java.sun.com/products/autodl/j2se" />
		
		<!-- Porperty used by the Pidstop framework to recognize web start applications. -->
		<property name="webstart" value="true" />
		<property name="DIR_GLOBAL" value="http://www.pidstop.com:80/energispillet_v2_2/" />
	</resources>
	
	<security>
		<!-- We need all permissions to write to file etc. -->
		<all-permissions/>
	</security>
	
	<!-- The file that holds the main(String[]) method to run -->
	<application-desc main-class="pidstop3.application.energy2.AppletEnergy" />
</jnlp>

Please note that www.energispillet.no is pointing to www.pidstop.com:80/energispillet_v2_2, cf. the jnlp-file above.

Can anyone of you help us with this?
Any idea where to start looking for a solution?

Thanks!