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I wonder if it is possibly on the other partition.
Maybe—I hadn't thought about that, since the other two posters didn't mention Boot Camp or Parallels. Don't try and run Disk Utility though.
Let's see if we can find this file in Terminal, but first empty everything you can from your Trash (if you're not ready to completely get rid of anything, move it to a "junk" folder instead).
Then, open the Terminal (from /Applications/Utilities) and
copy and paste the following into the Terminal window,
one line at a time, with a return after each line:
ls -aOlR .Trash
ls -aOlR /Volumes/*/.Trashes
Copy and paste the all the results from the Terminal window, including the commands, to a post here.