You probably opened the html-file directly from the local filesystem without using a Web-server.
Playing back flv-movies only works if the Movie is opened through a Web-Server because the Flash-Player of Macromedia only supports FLV-Playback through HTTP (or their streaming server) but not through local file access.
(I think they should have done it differently, though, and also support FLV-playback from local file access...)
Interview on the Linux Link Tech Show. Please select Episode 154.
DemoRecorder featured in Linux-User Magazine (in German)