This is an error produced by the web server software when it cannot find a default web page for your web site. In some ways it's not a bad error to receive because it means the web server is working, you just need to check a couple of things out.
- Are you connecting to the correct page and is there a default document?
If you have just put the web sites address into your browser e.g. http://www.<thedomain.com> and you get this error, try connecting to a page you know exists. For instance, if the home page is "index.htm" then try connecting to http://www.<thedomain.com>/index.htm.
If you are able to connect to the web site doing this, then it suggests that you need to update the "default documents" for your web site. This is a list of pages such as index.htm, default.aspx, index.php that you can tell the web server to use as the "default" document type for.
- Are you mixing different types of programmes in the same application pool?
Each web site on our server runs under its own "Application Pool". If you add a subdomain to a web site, that subdomain runs under the same application pool as the web site. If your site operates under, say, ASP.NET 4, and you create a subdomain that uses ASP.NET 3.5 then it will cause a conflict - one site may operate correctly for a while until one of the other subdomains is requested, then the error will be displayed. The same can happen when mixing PHP and ASP.NET 4 under the same application pool.