Take a look at the volume it's trying to install on. I noticed after installing 9.0.4 that the DVD player installer defaulted to my MacOS X HFS volume instead of the normal MacOS 9 boot volume (so of course I got the message you describe). Simply changing the target to my MacOS 9 volume fixed the problem. It took a second to notice this because I've never seen the installer default to the wrong volume before.
HTH...
Wayne Packard
wpackard@mindspring.com