Console.log does say "The file does not appear to contain a valid Automator workflow." But I'm not using Automator for anything. And Fetch is not a file, it's an application.
I was working on a document in TextWrangler (3.1), saved the document, then opened Fetch (4.0.2) from the dock. Automator opens instead, and I don't use Automator!
I'm running Tiger 10.4.11 on a 400MHz G3 iMac indigo.
I don't know if there's much difference between 500MHz and the iMac G3 400MHz I have, but just put in a 512MB PC-133 module and it runs just fine. (Seeing if I could do that after much research here. ;)) The PC-100s at that size were more pricy than I liked and scarcer than PC-133s.