I think I have stumbled on the problem....
Opening Synaptic Package Manager
Closing the error message shuts down Synaptic Package Manager.
I tried downloading the package again, and installing it, which seems to
have happened; however, the error message continues.
Then I managed to stumble onto another message...
software index broken use command:
sudo apt-get install-f
but I get another error message that there is no command -f