This is usually read from between <noscript>...</noscript> tag in your HTML file. Do you see such a tag in your HTML file? It will usually be towards the end of your file.
Thanks for your input Sudarshan. The script and noscript tags are present (Although I do not know how these lines got into my code.) Removing them eliminates the error message but the design view pane is still blank. Firefox option is set to enable Java Script. The html can be successfully previewed. Doesn't this confirm presence of Java Script? Here is a snippet of the code:
<!-- Provide alternate content for browsers that do not support scripting
or for those that have scripting disabled. -->
Sorry, this photo gallery requires that scripting be enabled on your web browser and that the Adobe Flash Player be installed.
<a href="http://www.adobe.com/go/getflash/">Download the Adobe Flash Player</a>
Also, Live View must be checked each time an .html file containing Flash is loaded; Is there a way to make Live View stay on by default?