General WordPress Related
From IThemes Codex
Author page Not Found
Problem: Clicking on the author name link (Ex.: http://www.leonardowood.com/author/Leonardo%20Wood/) in posts shows Page Not Found.
Solution:
The author link is supposed to be http://www.leonardowood.com/author/leonardo-wood/
Add the following to your theme's functions.php, reload your site twice.
global $wpdb;
$wpdb->query("UPDATE `{$wpdb->users}` SET `user_nicename`='leonardo-wood' WHERE `ID`='1'");
In the above replace "leonardo-wood" with your user nicename (User name in small case with hypens between spaces).
The above also assumes that ID of user in question is 1. This can be checked via phpMyAdmin in wp_users table.
After ensuring that this has been fixed, remove the above code from functions.php.
Source: http://ithemes.com/forum/index.php?/topic/9701-author-link-produces-404-page-not-found-error/#p45383