I can't trash files anymore, but only delete them directly
Solution 1:
Check the ownership and permissions on ~/.Trash.
mress:10039 Z$ ls -ld ~/.Trash
drwx------ 285 allbery staff 9690 Jun 28 16:53 /Users/allbery/.Trash/
My guess is it somehow ended up being owned by root, but there are other possibilities. If it's the owner, the fix is sudo chown $USER ~/.Trash ~/.Trash/.DS_Store.