Once you have found the problems, obviously, you’ll have to fix them, but usually that’s a simple walk in the park. Putting aside certain rarely encountered problems – for example, .htaccess issues – usually the reason is a bad link which can be easily fixed by correcting the given URL or using the aforementioned redirection methods.

However, if you are using a content management system, the troubleshooting process sometimes can be a bit more complicated, because you’ll have to find out whether the 404 error is caused by the content management system or the web server. If you are running a Wordpress site, presumably you already know, that WordPress processes its own internal rewrite array as a part of its permalinks structure. Obviously, first of all, you’ll have to verify if the given file exists, but if it does exist, and still, pulling up the URL in the browser results in a 404 error, you’ll have to find out whether the 404 error is caused by WordPress or the web server. Don’t worry, it’s really not a big deal and I am going to show you how to do it …

All you have to do, is to create a “test.html” file containing the words “server test” and a “test.php” file containing the “<?php echo ‘PHP server test’; ?>” command line. Upload both files and visit both pages (yourdomain.com/test.html and yourdomain.com/test.php) in your browser.

If their content (“server test” and “PHP server test”) is displayed correctly, you have no server-side problems and your 404 error is caused by WordPress. These WordPress-side issues usually are caused by taxonomy alterations, custom post types and wrongly coded or configured plugins.

As a first step you should reset the permalink array. Simply go to “Dashboard -> Settings -> Permalinks” and click “Save Changes”. If you are lucky, your 404 errors will disappear. If not, try to disable those plugins which are responsible for redirection and customized permalinks. If the problem still exists, I recommend you to install and use a debugger plugin like DebugBar or DebugThis to view the rewrite array and to see if the rewrite rule is responsible for processing “wrongly” your URL. Also, if there is no rule in place, WordPress usually will not process the request.

If you have problems while you are trying to identify and to solve your 404 errors on a WordPress site, you should use the 404-error-monitor plugin which logs 404 errors and 404 to 301 or all-404-redirect-to-homepage to redirect your visitors to another page whenever a 404 error occurs.

OK. Hopefully you have managed to fix your 404 errors in one way or another. At this point another logical question arises...

How often should you check your website for 404 errors?

Well, if you want to make a successful SEO for a WordPress website, I recommend you to do it at least once per month and if you have a complex site structure with frequent changes or content updates, you should probably do it every week. And of course, don’t forget to update your sitemap(s) every single time!

Finally, one last piece of advice: if you have changed your main domain, you’ll have to find a way to inform all your “partner” sites, so they can change the referring URLs, otherwise your precious inbound links won’t work!