Conflict with redirect

Love the idea of this plugin, but on installation it conflicted with a custom filter I have in my functions.php that redirects the login page (see the first post on this thread). After installing the plugin, all attempts to get to the login page went to a 404 error page.

I deactivated the plugin; no change. I uninstalled the plugin and no change. I had a look in the wp_options table and some data from the plugin is still there despite deleting the plugin.

Any help would be greatly appreciated!

http://wordpress.org/plugins/custom-pingback-email/