error code 4960 when saving a .plist
You are trying to create a launch agent with:


the wrong extension (plis)
in the wrong folder (/Library/LaunchAgents/ (suggested by the visible plists: java oracle/microsoft? updater, google keystone and teamviewer))
with the wrong app (TextWrangler)


TextWrangler isn't compatible with macOS 10.13. Download BBEdit or another compatible editor and try it again ;-)!