Click on the item in the Finder's sidebar with the house icon and verify that you are able to write to this folder in the Sharing & Permissions section of the Get Info window, and that it isn't locked; if it is already set this way and you get that error, open the Terminal in the /Applications/Utilities/ folder and run the following:
If you get a message stating that the folder exists, run the following:
sudo chown $UID ~/.Trash
chmod u+rwx ~/.Trash
The first command in the second set will prompt you for your administrator password; nothing will appear in the Terminal window while it is being typed. In either case, click on the Finder icon in the Dock with the Control and Option keys pressed, and relaunch it.