Using Flash Catalyst CS5.5 on a Mac, OS 10.6.8. Flv and F4v videos load and play on the browser in FC's Run Project, no problem. Opened in Dreamweaver, Live View, the page displays and plays the video. The same file, opened in Display in Browser, does not display the video, but does display the video controls. And likewise,when opened online, the page doesn't display the video, but does display the video controls. I've read in the Forums of similar problems, and am making sure that I use the Deploy to Web files exported from FC. No Joy. Everything else works great, though, and this is the last hurdle!
Do you have the debug version of the Flash Player installed or using Firebug in Firefox? Those might point out the source of the error (either code or a missing asset). A quick test would be to enter the full url of where the video file should be, the browser should try to download it. If you get a 404 error, then that is your problem.
Give those idea a try.
I ventured into code-land, briefly and with great trepidation. I opted to reinstall the whole suite, on a clean install system, on a wiped mac hardrive. That worked.
The problem had affected every Flv I tried to deploy to web, and appeared to originate at the Media Encoder point in the process. I was also using a third party hardrive, and had already experienced a problem associated with that.