Problem configuring USB support

[Ralph S]

I'm unable to get a USB drive to mount on my XP VM. I've read the various suggestions here and I'm in compliance with most of them, but my drive still won't mount and has problems that I haven't seen mentioned yet.

My VM is set to use one processor, I've downloaded and installed the recommended extension, and set up device filters so they look right. When I start the VM, the USB device list includes the Mac Keyboard and trackpad (grayed out) and the FaceTime Camera, Bluetooth USB Controller, and IR receiver (in black). When I plug in a USB drive it mounts on the Mac side, and show up in the Vbox device list in black. I think this is what I should see; is that right?

I select the drive in the Vbox device list in order to mount it. I get an error message that it failed to mount an unknown device, and the device list becomes empty and says "No USB devices connected." If I shut down the VM at that point it says "Windows logging off" and the window closes, but the Vbox settings pane still shows the VM as running. I can only get out of that by quitting Vbox, and then the next time I start it the VM shows as "aborted." It seems to start and run OK, though, and will shut down properly so long as I don't try to mount another USB drive.

The only advice I've found on this list that I haven't followed was to put my User name in the vboxusers group. I can't find any way to do that, and it appears from the manual to be only applicable to Linux hosts. Is that right? I'm running OSX 10.7.4 on a 2011 MacBook Pro, Vbox 4.1.18, and any further suggestions would be appreciated.

[Ralph S]

Update: I just read Perryg's advice to WesleydeSouza to uninstall and then reinstall Vbox and decided to give that a try. It worked -- sort of. My problem with the USB Device list disappearing and the VM hanging when I tried to shut it down has gone away, and things now work as I think they should -- almost. When I plug in a USB drive it now shows up in black in the device list, with a checkmark next to it. So it looks like it's mounted in the VM. But it doesn't show up in "My Computer" or "Windows Explorer," and I can't find any way to access the files. Where else should I look, and what else should I try.