I had a strange problem where USB devices were detected on the host system (Linux) but did not appear as available devices for a VirtualBox guest (XP). The strange thing was that I could use the devices normally on Linux, but they just didn't appear to the guests, not just XP but also a Debian guest.
I searched high and low for reports of the problem but nobody else seemed to have had it. And it was working before, although I was not sure if there was an intervening Linux kernel upgrade.
Finally in desperation I decided to reboot the system. Lo and behold, after that the devices became available to the guest. My best guess it that somehow the part of VirtualBox handling the USB forwarding got wedged. So give the old The IT Crowd advice a try.
