Hello,
Sorry for the problem with the 404 error that you’re seeing with your categories. Please check the URL that you’re seeing when clicking on the Categories. Also, make sure your Permalinks (in Settings) are set correctly. You may also need to reset them. This is done by going to Settings > Permalinks, Selecting PLAIN, then clicking on Save Changes. If you are using a Custom Structure, make sure to copy the structure BEFORE you click on Plain and save it. After you have backed up the custom structure (if needed), click on Custom Structure and set it back to the original settings, then save your changes. If you continue to have problems, then please provide us a URL for your site and provide the URL for the Category or Categories that are giving you the 404 error.