Java Web Start (javaws) refuses to run on snv_53 with following errors:

Version 1.5.0
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$ /usr/jdk/instances/jdk1.5.0/bin/javaws bugster.jnlp
Exception in thread "main" java.lang.UnsupportedClassVersionError: Bad version number in .class file
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:299)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:749)
        at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:847)
        at com.sun.javaws.Main.main(Main.java:76)

Version 1.6.0
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$ /usr/jdk/instances/jdk1.6.0/bin/javaws bugster.jnlp
X Error of failed request: BadMatch (invalid parameter attributes)
  Major opcode of failed request: 146 (MIT-SHM)
  Minor opcode of failed request: 4 (X_ShmGetImage)
  Serial number of failed request: 320
  Current serial number in output stream: 320


Only javaws version 1.4.2 (from /usr/j2se/jre/javaws/javaws) works ok in snv_53.

Information about my host:
$ uname -a
SunOS telcontar 5.11 snv_53 i86pc i386 i86pc
There is a bug with java upgrade from snv_52 to snv_53. As a result, the /usr/java link is point to Java 1.5 instead of Java 1.6. The bugid is 6492789.

The bugid 6492789 is already fixed in snv_54 and also Java 1.4.2 will be removed from the system during upgrade. Please LU your test machine to snv_54 and see whether you still had issues with javaws. This is not a upgrade bug but a java upgrade bug and the Java team should own this.