I have followed your 'Adding Extra Registration Fields' guide from this page on your website: http://www.jfarthing.com/development/theme-my-login/adding-extra-registration-fields, which is working fine.
The problem is that there are now 2 error messages for the default form fields (i.e. Username & Email) as I added these lines to my 'theme-my-login-custom.php' file in order to customize them. Both my customized text 'Username is a required field.' and the default 'ERROR: Please enter a username.' are displayed.
I see a similar question has been asked on this thread: http://wordpress.org/support/topic/change-the-error-message-text, and your answer is that it's part of the WordPress language file. I have downloaded and searched for the lines I'm trying to change and they do not exist.
So my question is how do I either customize the default error message text or remove the default duplicates completely?