FULL PRODUCT VERSION :
C:\>java -version
java version "1.6.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-beta-b59g)
Java HotSpot(TM) Client VM (build 1.6.0-beta-b59g, mixed mode, sharing)

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

EXTRA RELEVANT SYSTEM CONFIGURATION :
Browsers:
Firefox 1.5.01
Internet Explorer 6.0.2800


A DESCRIPTION OF THE PROBLEM :
A error occurred when I had entered my internet banking site (which uses an applet).
The error was a message poping up the browser:

"Java(TM) Plugin Fatal Error"
"The Java Runtime Environment cannot be loaded from <\bin\server\jvm.dll>"
and an "OK" button.

Then, I closed the browser, restarted the system, openned the browser again.

So, I tryed to show the Java Console, to see more detailed data. And the error happened again when I have clicked (in the Firefox or IE browser's, doesn't matter) in "Tools", "Java Console".

I started my navigator (for instance, Firefox)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
I upgraded my system from Java 1.4.2 to Java 1.6.0-beta
The error then started to occurs when I access a page that loads an applet (my internet banking site)

The error could be reproduced by just clicking (in Firefox, IE browsers) in "Tools", "Java Console"

See: forum: http://forum.java.sun.com/thread.jspa?threadID=536219
  See also the bug #5013503

There is A LOT of people out there with this problem. When upgrading, the Java installer is not doing it well.



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
It's is a blocker bug. It SHOULD NOT happen.
ACTUAL -
The error was a message poping up the browser:

"Java(TM) Plugin Fatal Error"
"The Java Runtime Environment cannot be loaded from <\bin\server\jvm.dll>"
and an "OK" button.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Java(TM) Plugin Fatal Error

The Java Runtime Environment cannot be loaded from <\bin\server\jvm.dll>

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
The workaround is described in the forum:

forum: http://forum.java.sun.com/thread.jspa?threadID=536219

For the lazy:

Remove C:\Documents and Settings\<user name>\Application Data\Sun\Java directory and it worked.