Java starter ikke

Jeg har i dag og i går haft problemer med at logge på internetbank og andre stader, hvor jeg skal logge på med nem-id.
Java starter ikke.
Hvad mon der er galt?

Følgende fejlmeddelelse kommer frem:

Java Plug-in 1.6.0_29
Using JRE version 1.6.0_29-b11 Java HotSpot(TM) Client VM
User home directory = C:\Users\John

----------------------------------------------------
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.ClassFormatError: Incompatible magic value 218774591 in class file dk/pbs/applet/bootstrap/BootApplet
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(Unknown Source)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Exception: java.lang.ClassFormatError: Incompatible magic value 218774591 in class file dk/pbs/applet/bootstrap/BootApplet