If you are a wordpress user or a wordpress developer then sometimes you may noticed a error when you are trying to view a post or page Like:
Error 404: NOT FOUND!
Your browser cannot find the document corresponding to the URL you typed in.
Sometimes it will happen when your permalinks is not accepted as valid on wordpress. If the permalinks settings is not valid then you can fix this error your wordpress admin panel. Just go to the settings tabs permalinks settings, then select a default settings. Then test your site.
If it seems your error is fixed then search on wordpress for any article about using permalinks to use custom permalinks.