Thanks for the reply to this. I'm sorry but I'm very new to IIS management. I don't think that the page is an asp.net page as there is no web.config file in the directory structure of the site.
From IIS manager if I right click on my comanpy's site and select properties/Custom Errors I find the custom 404 html file listed as the 404 error. This is the same on all the sub directories in IIS for my site. The only site it's working for is the root. I hope that helps and answers some of your questions.
Thank you so much for your time.