Error occurred when running VirtualBox, some box popped out.

$ VirtualBox
WARNING: The vboxdrv kernel module is not loaded. Either there is no module
         available for the current kernel (2.6.24-21-386) or it failed to
         load. Please recompile the kernel module and install it by

           sudo /etc/init.d/vboxdrv setup

         You will not be able to start VMs until this problem is fixed.
WARNING: The compilation of the vboxdrv.ko kernel module failed during the
         installation for some reason. Starting a VM will not be possible.
         Please consult the User Manual for build instructions.

$ sudo /etc/init.d/vboxdrv setup
 * Stopping VirtualBox kernel module                                                                                                                                                     done.
 
Recompiling VirtualBox kernel module                                                                                                                                              
 * Look at /var/log/vbox-install.log to find out what went wrong

$ tail /var/log/vbox-install.log
Makefile:142: *** Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR= and run Make again.  Stop.

$ sudo KERN_DIR=/usr/src/linux-source-2.6.24   /etc/init.d/vboxdrv setup
 * Stopping VirtualBox kernel module                                                                                                                                                     done.
 
Recompiling VirtualBox kernel module                                                                                                                                                  done.
 
Starting VirtualBox kernel module                                                                                                                                                   *  done.

OK, it works.

$ dpkg -s virtualbox-2.0 | tail
Conflicts: virtualbox
Conffiles:
 /etc/init.d/vboxdrv 6e3cb8dd230d768740ce0c6e0ae6a86c
 /etc/init.d/vboxnet a3828b76a2fdfc0fb6908f2a76c86550
Description: Sun xVM VirtualBox
 VirtualBox is a powerful PC virtualization solution allowing you to run a
 wide range of PC operating systems on your Linux system. This includes
 Windows, Linux, FreeBSD, DOS, OpenBSD and others. VirtualBox comes with a broad
 feature set and excellent performance, making it the premier virtualization
 software solution on the market.