I started to have a lot of problems with VirtualBox on my Windows 7 box about two weeks ago. Whenever I tried to shut down a virtual machine, it crashed, and the state of the VM could not be saved successfully. The new version of VirtualBox came out around the same time I had the problems, so I upgraded to the new version: 3.1.6.
After upgrading, the problem became worse. I could not start any virtual machines at all. I always got this message:
My first reaction was to reinstall the application. However, a forum post suggests that the repair option in the setup program might be able to fix the problem. Following the instructions, I re-ran the installation program and clicked on the Repair button and let the setup program to repair it.