If you're typing that exactly as is in a terminal window, then you may have better luck if you prepend 'sudo'.
But it might be something that the Finder's waiting on, so killing it alone may not be enough. My money's still on Spotlight racing through the disk trying to set up its database of meta-info.
Before you plug it in again, fire up Activity Monitor and watch the 'All Processes' list when you connect the drive. Does anything shoot to the top and stay there?' (click the column heading to sort by CPU %).