FULL PRODUCT VERSION :
Java Plug-in 1.6.0-beta2
Using JRE version 1.6.0-beta2 Java HotSpot(TM) Client VM

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
With my applet (signed, obfuscated) consisting of many jar files, if "Keep temporary files on my computer" is ticked on in the Java Control Panel/Temporary Internet Files/Settings then the exception (see below) is thrown.

If ticked off, then the applet works as excepted.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See description.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
See description.
ACTUAL -
See description.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.IllegalStateException: zip file closed
at java.util.zip.ZipFile.ensureOpen(Unknown Source)
at java.util.zip.ZipFile.getEntry(Unknown Source)
at java.util.jar.JarFile.getEntry(Unknown Source)
at com.sun.deploy.cache.CachedJarFile.getEntry(Unknown Source)
at java.util.jar.JarFile.getJarEntry(Unknown Source)
at sun.misc.URLClassPath$JarLoader.getResource(Unknown Source)
at sun.misc.URLClassPath.getResource(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at sun.applet.AppletClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.applet.AppletClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at nz.co.nbnz.dlink.common.distributable.types.NamedAccounts.fromPacked(NamedAccounts.java:75)
at nz.co.nbnz.dlink.online.applet.domestic.batch.comms.DownloadParameters.run(DownloadParameters.java:117)
at nz.co.nbnz.dlink.online.applet.domestic.batch.comms.CommsThread.stateLoadParameters(CommsThread.java:138)
at nz.co.nbnz.dlink.online.applet.domestic.batch.comms.CommsThread.run(CommsThread.java:380)

REPRODUCIBILITY :
This bug can be reproduced always.

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Can't provide snapshot of source code to replicate problem, but will allow access to our production environment and source tree if required. Contact me for access instructions.
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CUSTOMER SUBMITTED WORKAROUND :
Tick off "Keep temporary files on my computer" in the Java Control Panel/Temporary Internet Files/Settings.