I love Virtualbox and have been using it for several years. I use it to experiment with new linux distros and learn more about linux. After updating to Mavericks, I had a few issues, so I uninstalled and re-installed Virtualbox. Things seemed to be working fine, problem solved, so I thought. When I rebooted my machine, Virtualbox was no longer working, so I reinstalled it, boom, it worked again. I just thought that something went wrong the frst time. I discovered that after a clean install, it would work fine, until you rebooted. I did some research and learned that there was an issue with the old kernel files not being removed and had to be done manually. The documentation I found seemed a bit complicated, so I kept searching and found a great solution from a blog by Jonathan Ocab.
First, if you already have it installed, uninstall it. Then go grab a fresh download and install it, once it’s installed, go download the extension pack. Next you need to go to /Library/Extensions and run the following code sudo rm -rf VBox*.kext then reboot.