Why does this happen with AppleScript?

AppleScript sends Apple Events to control apps. If the target app is not running or crashes, the event cannot be delivered, causing -600.

How do I rebuild Launch Services?

Run the lsregister command in Terminal with -kill -r flags. This forces macOS to re-scan all applications and rebuild the database.

Warningsystem

Mac error -600 occurs when the system tries to communicate with a process that no longer exists, common with crashing apps and Apple Event failures.

Error -600 maps to procNotFound — the target process for an Apple Event cannot be found
Apple Events are the inter-process communication mechanism in macOS
Occurs when an app crashes or quits while another app tries to communicate with it
Common with AppleScript, Automator, and apps that use inter-app communication
Launch Services database corruption can cause persistent -600 errors

1Open the target application manually before running the AppleScript or automation
2Rebuild Launch Services database: /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user
3Restart the Mac to clear stale process references
4Check Console.app for crash logs related to the target application
5Reinstall the application if crash logs show consistent failures