Thank you for the hint. I do indeed have a PCI ATI Mac Radeon card
installed in the G4 as a second monitor (NTSC). Since it does not
support Quartz Extreme somehow the Quartz Composer must have seen
it and did not wanted to run the "Image With Movie." I disconnected
the S-Video cable to the Radeon and restarted so it would no longer
be listed as a display. The patch now works fine. I wonder if all
the video cards in the computer must support Quartz Extreme with a
mix of them causing problems?
It's actually a QuickTime issue: all displays must support Quartz
Extreme and this basically means multiple displays are only allowed
if driven from the main video card.
