It might be because of multiple reasons.
Possible reasons and its resolution might be:
1. If you are running in IE and you are not able to view flash content it might block Flash Content playing in it.
To play the flash content, just add ActiveContent.js file and import this file from your HTML.
2. If you are running the .fla file locally on the machine and you are loading a movie from network, security sandbox violation occurs.
To resolve this, you have to copy the file in trusted folder. Otherwise you have to trust this file via Flash Security settings manager.
Many thanks for your reply.
No, I am just trying to open the HTML file locally. In the past, I have simply clicked on File | Publish in the MX 2004 application and it generates a working movie in an HTML file (using IE). But recently, as I say, although the HTML file is generated, the movie does not show in the browser.
The files I have downloaded are AC_ActiveX.js and AC_RunActiveContent.js. Are they the files you mean? And where do I install them to? The same directory as my FLA file?
Yes, You have to copy the AC_RunActiveContent.js in the same folder where you have the html file. In the HTML file, please make sure you imported the AC_RunActiveContent.js file.
The above solution works if it is because of the active content blocker.