The problem is that it can't the DVD player software. WC4 requires an MCI-based DVD player, which is an interface that Microsoft deprecated around the Win2k era.
You'll probably need to get old Win95 drivers and install 95 or 98 on your system to get it to work properly.
(I got that "Can't find movie" error when I rebooted into Win98 a while ago - I reinstalled WinDVD 2 which came with MCI DVD drivers, and it worked, somewhat - it doesn't get the end of movie signal.)