I have exactly the same issue.
I guess you refer to http://www.jfarthing.com/development/theme-my-login/general/
Page ID
This should be the ID of the WordPress page to be used as the main login page. It is imperative that this page contain the [theme-my-login] shortcode. It is also as equally important that this field point to the correct page ID. An incorrect value here will wreak havoc across your whole login/registration system and is the number one cause of malfunctions with the plugin.
I even made a search in the database if I find somewhere the id of the page stored to change it manually.
Regards
Cedric
Yes, I just went ahead and set up the registration without including a page ID. Everything has worked fine so far.
