trash can is empty but looks full

Try logging out and logging back in, if the iMac has not been otherwise restarted since you noticed this problem. That will restart the Dock application.

Put an empty folder, or any file you don't need in the Trash, so there is something to empty. Then empty the Trash.

I finally was able to empty my trash after trying everything listed above.

Here's all of the things that didn't work (for me), and the odd thing that I did that did work:

I kept getting the error message: The item ".Trash" is in use right now and cannot be opened.
I was about to lose my mind.

I have a program called "Smart Trash"...nope.
I tried "Super Empty Trash"...nope.
I ran some terminal commands followed by a Repair Disk Permissions...nope.
Option-Empty...nope.
I booted VMWare Fusion / XP, and did a CHKDSK...nope.
I tried creating an empty folder and dragging the files (17 of them) into the empty folder, then deleting the empty folder, but my computer wouldn't let me pull the files out of the trash and move them to the new folder.
I put the files into A Better Finder Rename and tried to rename them...nope.

Then, I did something that you'd never think would solve the problem, but for some reason it did.

I opened up the trash, did a Cmd-A to select all, then a Cmd-I to find out how (collectively) big all of these files were and when my Mac tried to access the files to see their size, they disappeared.
I have no idea why that was the thing that worked, but my Trash is empty and the paper in my trash icon is gone.

Just thought I'd share this because I know there are others out there that have tried everything as well. I'm not promising this will work for you, but what have you got to lose, right?

J.

If the icon still shows that you can always go into your trash folder and delete everything.

cd .Trash/

and type rm -rf *

and that might get rid of it, if that still fails you can always delete your com.apple.dock.plis in ~/Library/Preferences/ and as well the com.apple.dock.db and it should reset your dock back to default.

When you click on the Trash icon in the Dock, it should show you the content of the Trash. Are there any files in the Trash?

To +force empty+ the Trash, hold the Option key when you empty the Trash.