Hi waypylant,
Welcome to the Sony Community!
How were you updating the program? Are you updating it through the software itself or downloading a new version? The message may pop up when the software is still running and has not been properly closed. I suggest restarting your computer before downloading the latest version of PlayMemories Home. You can also uninstall the older version by going to the Programs tab in your computer (inside Control Panel for WIndows, Applications in Mac) and install the newer version after. Restart your computer once you've uninstalled PMH.
If my post answers your question, please mark it as "Accept as Solution". Thanks_Mitch