tested build: http://j2se.east/plugin/1.6.0_04-nightly/2007-08-15.23_16

1.Installed Kernel JRE on a clean machine.Installation is successful and BackgroungDownloader started immediately.
2.Launched cacheviewer and Notepad appln (http://java.sun.com/products/webstart/apps/notepad.jnlp)
3.Uninstalled Kernel JRE.Got the Virtual machine Launcher Error dialog "Main Calss Not Found.Program Will Exit".(attached screen shot kernel_uninstall_16aug.jpg)

I got the same error dialog in these scenarios also,but this is not consistent.
When I am trying to reproduce it,I am getting different issues.

1.Installed Kernel JRE on a clean machine.Installation is successful and BackgroungDownloader started immediately.
2.Launched cacheviewer (javaws -viewer) successfully.
3.Uninstalled Kernel JRE.Got the Virtual machine Launcher Error dialog "Main Calss Not Found.Program Will Exit".(attached screen shot kernel_uninstall_16aug.jpg)
4.Tried to reproduce this many times on the same machine.(4-5 times ). it works fine and I couldn't reproduce the issue .

Another scenario :(attched screenshort scenario.jpg & scenario_uninstall.jpg)
1.Installed Kernel JRE on a clean machine.Installation is successful and BackgroungDownloader started immediately.
2.Tried to launch notepad application (http://java.sun.com/products/webstart/apps/notepad.jnlp)
This DID NOT launch notepad application and I got the same Java Virtual machine Error dialog with "Main Calss Not Found.Program Will Exit".
3.After this I am not able to launch any javaws aplication and uninstallation gives the webstart error