This error occurs if your content management system is poorly developed. It says that the file was not found. However, the correct form of that error would be a 404.
This is the most search engine friendly method for redirecting web pages or entire websites, which is referred as Moved Permanently . Moreover, it’s the safest option if you think of changing file names or moving pages around. Apart from that, it will also be useful for any canonical issues you experience.
The equivalent to the 301 Redirect method is this one here. Basically the old URL is redirected to a new one. This redirect form is just temporary and advisable not to avoid.
This error refers to “Page not found error”, which means the server couldn’t find the requested page. Make sure that files that actually exist provide a 200 error and requested file that do not exist give a 404 error.