If you are restricting posting ads to registered users only and your WordPress login page is different from the standard wp-login.php?action=login, you will need to tell the system the location of your login page so users are directed to the correct location to login. To tell the system the location of your login page you need to go to your classifieds admin options page and click the “Registration Settings” tab. Under the “Registration Settings” tab, look for and fill out:

Post login form to [Value should be the full URL to the WordPress login script. Example http://www.awpcp.com/wp-login.php **Only needed if registration is required and your login url is mod-rewritten ]

Above it says only needed “if registration is required and your login url is mod-rewritten”, it should also say “or if your login page URL is otherwise different from the WP standard.