You have been creating so many new pages recently you can count on the fact that you very well may have renamed a file the wrong name. No worries, create custom error pages for your customers to see. Save yourself a few minutes of finding out of date pages and save your site visitors some headaches by reading the following article about creating custom 404 error pages.
While there is no substitute for making sure all of your links are working correctly before your site is live, this is a nice little website developer insurance tactic if you will. Be smart, check your links with the very helpful W3C link checker.