A 501 is an HTTP status code for not implemented. This status code is received when the web server does not support the facility required.
A 501 error is not something you can fix, but rather will require a fix by the web server admin who manages the website and server you are trying to access.
Web server overload
If the server you’re attempting to load is experiencing high demand, it may be unable to complete your request and generate this error. If you’re experiencing this error on a page you know is functional, try loading the page again after a few minutes. If that is unsuccessful, try loading the page again later that day or the next day.
Web server errors
Visitors may also encounter this error when a web server does not properly respond to a browser’s request or the program making the request.
Web server out of date
Finally, in some rare situations, the web server may need a software upgrade to properly communicate with your web browser or program.