Kernel upgrade in Ubuntu usually is a straight forward process. However, last night following a kernel upgrade from 2.6.24-19 to 2.6.24-21, Virtual Box on which my Windows XP is loaded came up with a spawning error. This prevented Virtual Box from loading Windows XP.
Googling for a solution, I found the following that resolved the problem.
Execute the code below in 'Terminal' after every kernel upgrade to ensure that Virtual Box works.
sudo /etc/init.d/vboxdrv setup