Please try resaving your permalink settings.

If it doesn’t resolve the issue then please reset your site htaccess file as described on the following pages.

http://www.bordercrossingmedia.com/2009/01/how-to-restore-your-wordpress-htaccess-file/

https://www.tipsandtricks-hq.com/how-to-reset-the-htaccess-file-of-your-wordpress-site-using-ftp-8527