FULL PRODUCT VERSION :
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Client VM (build 1.6.0_01-b06, mixed mode, sharing)

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

A DESCRIPTION OF THE PROBLEM :
Shortcut stops working if jnkp file of a signed jar changed on server.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Sign a Java application.
2. Install a Java Webstart deployed software via its online jnlp, making sure the jnlp file contains:
 <offline-allowed />
     <shortcut>
      <desktop/>
    </shortcut>

3. Allow the install of the shortcut.
4. Change something in the jnlp file. ie. Change SEVERE to WARNING in demo JNLP.
5. Try to run the application with the shortcut.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Exp. result: the application starts.
ACTUAL -
Act. result: an error message appears: Unable to launch the application

ERROR MESSAGES/STACK TRACES THAT OCCUR :
CouldNotLoadArgumentException[ Could not load file/URL specified: C:\Documents and Settings\John\Application Data\Sun\Java\Deployment\cache\6.0\34\38fa84a2-422f80a7]
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)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
<?xml version="1.0" encoding="ISO-8859-2"?>
<jnlp spec="1.0+" codebase="http://example.com" href="myapp.jnlp">

  <information>
     <title>Title</title>
     <vendor>Vendor</vendor>
     <homepage href="index.html" />
     <description>Description</description>
     <offline-allowed />
     <shortcut>
      <desktop/>
      <menu submenu="My Application"/>
    </shortcut>
   </information>

  <resources>
     <j2se max-heap-size="128M" version="1.5+"
href="http://java.sun.com/products/autodl/j2se"/>
     <jar href="myapp.jar" main="true" />

<property name="myapp.log.level" value="SEVERE"/>
</resources>

  <application-desc main-class="MyApp"/>

  <security>
     <all-permissions/>
  </security>

</jnlp>
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Uninstall the application and install again.
Same issue reported by a CAP member:

Encountered a problem with their deployments with Sprint and Electronic Arts that happens with the latest Java 6 JRE. Both accounts are using the desktop icon shortcut to launch their respective applications, and both are encountering this bug -- which renders their desktop icons non-functional with cryptic user-visible error messages.
the CAP member can still reliably reproduce it on the early access release, and so can some of
the other users
based on the comments. Attached is their a reproducible test case:

http://content.mpowerplayer.com/hosting/java.com/