I don’t know, it fix an error in WP 3.4. It is possible that this error cause the issues with the other plugins.
Hello, since WP 3.4 get_userdatabylogin function is deprecated, and theme-my-login uses it, while the author fix it, you can modify the line 306 of class-theme-my-login.php in the includes folder of the theme.
Now it is:
if ( $user = get_userdatabylogin( $user_name ) ) {
it should be:
if ( $user = get_user_by( 'login', $user_name ) ) {
