Java error message - Bad version number in .class file

Question

I get the  error noted below in Safari, Firefox, and Chrome when I try to view java containing web pages.
Specifically this page: http://aviationweather.gov/adds/tafs/java/
My Java Preferences are as follows
My OS is 10.5.8
Thanks!
Java Plug-in 1.6.0_26
Using JRE version 1.5.0_30-b03-389-9M3425 Java HotSpot(TM) Client VM
User home directory = /Users/ernest
c:   clear console window
f:   finalize objects on finalization queue
g:   garbage collect
h:   display this help message
l:   dump classloader list
m:   print memory usage
o:   trigger logging
q:   hide console
r:   reload policy configuration
s:   dump system and deployment properties
t:   dump thread list
v:   dump thread stack
x:   clear classloader cache
0-5: set trace level to <n>
java.lang.UnsupportedClassVersionError: Bad version number in .class file
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:676)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.ja va:25)
    at java.lang.reflect.Method.invoke(Method.java:592)
    at sun.plugin2.applet.Plugin2ClassLoader.defineClassHelper(Plugin2ClassLoader.java :1014)
    at sun.plugin2.applet.Plugin2ClassLoader.access$100(Plugin2ClassLoader.java:69)
    at sun.plugin2.applet.Plugin2ClassLoader$2.run(Plugin2ClassLoader.java:991)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Plugin2ClassLoader.java:9 55)
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Applet2ClassLoader.java:134)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Plugin2ClassLoader.java:250)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Plugin2ClassLoader.java:180)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Plugin2ClassLoader.java:161)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
    at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Plugin2ClassLoader.java:675)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Plugin2Manager.java:3046)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.ja va:1498)
    at java.lang.Thread.run(Thread.java:655)
Exception: java.lang.UnsupportedClassVersionError: Bad version number in .class file

Answer 1

Hi, thank you for the reply.  However, java is definitely enabled on my computer, on all my browsers.  In fact, if I go to the SUN website and run the java test, I get that all is OK.
I think it may have something to do with the .class (maybe in .jar-file) compiled with a higher version of java than the virtual machine trying to run it. 
The example I found (google search) is .class-file that is compiled with JDK 6 and I am trying to run it with 1.4 JVM.
There is some software error going on somewhere... but I do not know enough to fix it.
Many thanks for all your help