While the initial background downloader is running (background downloader launched by java installer), Launching control panel gives "Main Class Not Found.Program Will exit".(KernelDownloadUrl is used)
This error is coming in XP also.(129.158.229.123, vnc password :vnc )

I can reproduce the problem in my XP machine too. It seems like it's caused by:

java.lang.IllegalStateException: error acquiring mutex
       at sun.jkernel.Mutex.acquire(Native Method)
       at sun.jkernel.Bundle.loadReceipts(Unknown Source)
       at sun.jkernel.Bundle.updateState(Unknown Source)
       at sun.jkernel.Bundle.isInstalled(Unknown Source)
       at sun.jkernel.DownloadManager.doGetBootClassPathEntryForResource(Unknow
n Source)
       at sun.jkernel.DownloadManager.access$500(Unknown Source)
       at sun.jkernel.DownloadManager$3.run(Unknown Source)
       at java.security.AccessController.doPrivileged(Native Method)
       at sun.jkernel.DownloadManager.getBootClassPathEntryForResource(Unknown
Source)
       at sun.jkernel.DownloadManager.getBootClassPathEntryForClass(Unknown Sou
rce)
       at java.lang.ClassLoader.findBootstrapClass(Native Method)
       at java.lang.ClassLoader.findBootstrapClass0(Unknown Source)
       at java.lang.ClassLoader.loadClass(Unknown Source)
       at java.lang.ClassLoader.loadClass(Unknown Source)
       at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
       at java.lang.ClassLoader.loadClass(Unknown Source)
       at java.lang.ClassLoader.loadClassInternal(Unknown Source)