Thanks, Stan.
I followed the link in your suggestion. The suggestions for rebuilding the Launch Services file on the Google page relate to older versions of OSX, and were dated 2014. They suggested locating and deleting the following: com.apple.LaunchServices.plist, but in my preferences folder on Sierra this file does not exist. When I search for LaunchServices in Spotlight, I get no result and also this information:
"This error indicates that there was a problem with installation. Unfortunately, Xcode does not actually print the contents of the error message that would give you more insight, but you can look at ~/Library/Logs/CoreSimulator/CoreSimulator.log to see the rest of the error details. There will also be more information about the problem in the simulated device's system log (~/Library/Logs/CoreSimulator/[Device UDID]/system.log); look for messages from installd around the time of the error).
Common causes for this include bundles missing an Info.plist, missing keys within your bundle's Info.plist, or values for some keys in the Info.plist not being allowed.
If your app's Info.plist does not contain a valid CFBundleVersion key/value pair, it is possible that your app may install correctly the first time but fail to update. Many users seem to work around this by doing a "Reset Contents & Settings" after each install, but it would be better to fix the root cause by setting an appropriate CFBundleVersion in the Info.plist. I believe iOS 8.2 now correctly returns an error on the first install in this case rather than just on updates, so hopefully this problem will be more obvious now."
None of this means much to me, but it is possible that in Sierra the LaunchServices .plist has been superseded by something else.
BRIAN