Browsing to a child portal without entering a final page name in the url should ordinarily deliver the default home page of the child portal. But sometimes you get the 404 page not Found error instead.
For example: http://SomeDomain.com/MyChildSite
Should return http://SomeDomain.com/MyChildSite
/home.aspx - assuming home.aspx is the designated home page on this site.
If instead you receive a 404 Page Not Found Error, then it could be that there is a folder and a file missing from the root of your DNN installation.
There should be a folder in the root folder with the exact same name as the child web. And in that folder is a copy of the file subhost.aspx that has been renamed to default.aspx. Look to see if they are missing. If so, make the folder and put the file in there. If you have another child web, you can hopefully grab a copy of that file from that child portal folder. Just copy and paste it. You don't have to change anything inside the file.
There is probably other reasons for this error. I hope this works for you, but if not, keep googling.
Here is a reference to this topic. http://books.google.com/books?id=eS...04&f=false