With the new version of VirtualBox (4.0.0) comes a new feature called Extension Packs. These will contain various additions like PUEL USB and others.
If you have the USB enabled when you update to version 4.0.0 and try to start the guest you will receive an error until you turn off USB or install the Extension Pack.
To install the Extension pack you down load and save it to your hard drive and then open the VirtualBox main program. Click on preferences and on the left side click Extensions. On the right side, click the add package icon and then open the folder that has the extension and click to install it.
Additionally you can install the Extension Pack from the command line using VBoxManage.