Hello,
That error commonly happens when there is a permissions error, the .htaccess file is missing, Or the web server is not configured to allow a .htaccess file to be used. I would recommend ensuring the default WordPress .htaccess file is present in your document root and that your permissions are correct. You can find a default .htaccess file here. If your .htaccess and permissions are correct i would recommend contacting your host to ensure the web server is configured to use the .htaccess file.
Best Regards,
KyleM