If you are using Ubuntu (or probably other versions of linux as well) and the OSE version of Virtualbox, then after upgrading you might find that your virtual machine images no longer run.
The solution is really simple.
1. Uninstall VirtualBox OSE
2. Go to the Official VirtualBox Downloads Page and download the correct version for you platform. You should find that it runs your images fine and wont be susceptible to this upgrade problem in future.
another problem solved