Guest OS cannot see USB even after selecting it in VirtualBox

I have the latest VirtualBox 4.0.8 (from the VirtualBox website), including the extension pack, running on Ubuntu Lucid 10.04. My user is a member of vboxusers.

The guest OS is Windows XP (32-bit).

Everything works -- except the USB. In the USB settings. I have set the default filter (to allow all USB devices). While the guest is running, I go to Devices > USB Devices and select the device (it's a simple USB stick formatted as FAT32).

Although the device is automatically unmounted from Ubuntu, Windows XP fails to see it (normally XP would have a little dialogue about installing a new device and then show the icon to safely remove a drive. It does not do this).

Any ideas how to solve this problem, so my guest Windows XP can see the USB stick?

A bit of Googling told me to look in Control Panel > System > Hardware. I found the USB with a yellow question mark. Right-click > install driver did the job. Thank you. I hope this helps someone with the same problem.

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