Q: I can not empty the trash.

Launch the Terminal app on your Mac by either searching for it in Spotlight or locating it in the Utilities folder under Applications.

Type in the following command: "sudo rm -rf ~/.Trash/*" (without quotes) and then hit Enter on your keyboard.

You may be prompted to enter your OS X user password. Type it in and then hit Enter on your keyboard.

You should now be returned to the main user prompt in Terminal. Notice the Trash in your dock which should now be empty.

http://www.imore.com/how-force-empty-trash-your-mac-using-terminal

http://support.apple.com/kb/ht1526 You can't empty the Trash or move a file to the Trash

What to do when the Trash won’t empty

First, whenever a question like yours is posted on this site, someone is likely to respond with very bad advice to empty the Trash in the shell. Never do that. It's dangerous, unnecessary, and as you've discovered, it doesn't always work.

The files in the Trash are on an external drive, or on another partition of the internal drive. If you have an external drive that is formatted for Windows (as NTFS), boot into Windows or connect the drive to a PC and empty the Recycle bin.