Can't disconnect USB disk

XP Pro SP2, 512M, Pentium M

I have an external hard drive connected through the USB port.

When I click on the icon in the taskbar and tell it to disconnect the drive
so that I can unplug it I receive a message that the drive is busy, try
again later. Waiting until later changes nothing.

When I hibernate, unplug it then start up it tells me it cannot find the
drive's MFT (e:\$mft)

What setting can I change to make it so that I can safely unplug the drive
either with the taskbar icon or by hibernating and unplugging while the
machine is dormant?