I'm stumped. It definitely sounds like you're having trouble with the ACGI Dispatcher. A few last things to try:
- Make sure you're using the .acgi extension on your script. Do a "get info" on the file; it may appear that the extension is correct, but in reality the filename is omnifocus.acgi.app.
- Re-install ACGI Dispatcher
- Disable ruby/lighthttpd. I have no idea why this would be conflicting with ACGI Dispatcher, but who knows.
Other than that, I'm out of ideas. If you do solve the problem, I'd love to hear details.