Are you sure that you have the latest version of Java (www.java.com) installed on your computer and you are using the latest version of the web browser that you chose to use?
Playing the computer??

I have the same problem on Windows Vista system.
Previously I had an older version of Java 1.5.0_12,
but of course I installed the latest version 1.6.0_20.
Nothing helps. Same errors are for Firefox and Internet Explorer.
I've just registered to the website and everything looks very nice to me,
however I am a bit shocked, that this thread has been started on 6th December 2009
(half year ago!) and there are still same problems with the chess board against computer !!
Below I attached some info from Java log window: separately for 1.5 and 1.6 versions.
The errors may suggest that there are some badly compiled applets.
Can anyone from the website service check why there are such strange errors ?
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Here is what I found in the Java 1.5 log window:
Java Plug-in 1.5.0_12
Using JRE version 1.5.0_12 Java HotSpot(TM) Client VM
User home directory = C:\Users\tomek
java.lang.ClassFormatError: Incompatible magic value 1008813135 in class file javax/swing/SwingWorker
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at sun.applet.AppletClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.applet.AppletClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at sun.applet.AppletClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.applet.AppletClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at com.chess.applet.ChessApplet.init(ChessApplet.java:76)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
-------------------------
HERE - ERRORS from Java log window after 1.6 installed:
Java Plug-in 1.6.0_20
Using JRE version 1.6.0_20-b02 Java HotSpot(TM) Client VM
User home directory = C:\Users\tomek
java.lang.RuntimeException: java.lang.ClassFormatError: Incompatible magic value 1008813135 in class file com/chess/chessboard/MoveListener
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassFormatError: Incompatible magic value 1008813135 in class file com/chess/chessboard/MoveListener
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 java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
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 java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.defineClassHelper(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.access$100(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Unknown Source)
at java.lang.Class.getConstructor0(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$12.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Exception: java.lang.RuntimeException: java.lang.ClassFormatError: Incompatible magic value 1008813135 in class file com/chess/chessboard/MoveListener
I tried to play a game against the computer but no board appears, onl a small red X in the L hand corner. I have tried the suggestions of the HELP center but no change. Any help is appreciated......