Error message when unmounting external drive

I have an IDE hard drive that I use as an external drive, by way of an IDE to USB cable. It mounts fine, automatically. But when I right click on the desktop icon for the drive and select "Safely Remove Drive", ever since I upgraded to Lucid, I get the following error message in a pop-up window:

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Error detaching: helper exited with exit code 1: Detaching device /dev/sdb
USB device: /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1)
SYNCHRONIZE CACHE: FAILED: No such file or directory
(Continuing despite SYNCHRONIZE CACHE failure.)
STOP UNIT: FAILED: No such file or directory
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The drive seems to unmount and I can just ignore this message, but I wonder if anyone can help me figure out what is causing it and make it stop popping up.