Under Mac OS X 10.12.1 aka macOS Sierra attempting to put files into the trash results in an error message:
The operation can't be completed because one or more required items can't be found. (Error code -43)
Currently a solution can not be googled that well: As general as the error message sounds there is a large heap of well meaning system care advice.
In my situation the problem seems to have been caused by no cleanly un-mounting CF cards and/or external hard drives.
A reboot makes the issue go away. Nothing more and nothing less required.