That’s a simple htaccess/permalink error, it’s a quick fix:
- Login to your WordPress Admin > find Settings > Permalinks
- Simply click the Save Changes button (this will flush the rewrite rules)
- That’s it, you should be all set.
If you’ve already tried the above, we’ll need to take it one step further:
- Connect to your server via FTP and deleting the .htaccess file (if you’re unsure how to do that, your hosts support can help)
- Go back to your WordPress Admin > Settings > Permalinks > Set to Plain > Save Changes > Test the front end of your site
- Then go back to Permalinks > set to Post Name
- Save Changes, and you should be all set.
For more information on this problem have a look at this article.