I get the same exact error message if I try to open the file (i.e. not the URL) using my browser (both with MSIE and Firefox).
Make sure you are accessing the page through HTTP; the address bar should say something like http://localhost/rssreader/rssajax.html. If it doesn't start with "http://" you're simply viewing the HTML file in your browser, so client-server communication is not possible.
I want to thank you very much for the info you listed here, I have been trying every thing possible to find out how to correct a Javascript error (0) for a day and half and all it took was to type HTTP:// before the address, why doesn't Java explain this in their site, Again thanks very much!!!! Bill