If you have just migrated to VirtualBox 4.0, you may encounter the following error if you are using the Save Machine state option and you have kept the USB controller option for the EHCI Controller:
To avoid this error, simply shutdown or power off the VirtualBox guest machine and then you can either:
You can now restart the VirtualBox guest machine(s) and use the Save Machine State every time you close it without receiving any errors or experiencing any further issues.
Enjoy
Links:
[1] http://pulse.veltsos.com/category/it/software/foss
[2] http://pulse.veltsos.com/category/it/tweaks
[3] http://pulse.veltsos.com/category/it/virtualization
[4] http://linux.philosweb.com/drupal/system/files/SNAGHTML1c9fd1c.png
[5] http://www.oracle.com/technetwork/server-storage/virtualbox/downloads/index.html#extpack
[6] http://linux.philosweb.com/drupal/system/files/SNAGHTML1c528dd.png
[7] http://linux.philosweb.com/drupal/system/files/SNAGHTML1c6378c.png