I just upgraded to Linux Mint 16 KDE, and installed Virtualbox, and cannot enable the USB. I did not have any problem doing this with Linux Mint 15 KDE. On Linux Mint 15 KDE though, first you had to go to the user and check the box for Virtualbox, in order for this to work. How ever, they have taken that option out on Linux Mint 16 KDE, and you cannot put a check mark on the Virtualbox or anything else. There must be another setting that I'm not aware of.
When you go to the settings, you see that the USB controller box is checked and enabled. Needless to say that I have already installed the Virtualbox extension pack. So when I start the Windows 7, and click on devices, you see that “no USB devices connected" (grayed out). Therefore, I think the problem is within the user interface, because you have no option of clicking on anything. As I mentioned this was no problem on Linux Mint 15 KDE, because you could go to the user and click on all kinds of settings and check the boxes you want. I also tried the latest version of Virtuabox 4.3.6 from Oracles website with the same result. The current version that I'm using is 4.3.0.
I am totally stuck. Any idea or suggestion will be greatly appreciated.