The admin section user register no longer works!

If you've tweaked your user register form, and now for some reason you can't add a new user via the admin section. It's entirely possble that you've changed the submit buttons value, like:

/**
* Implementation of hook_form_alter().
*/
function mymodule_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == 'user_register') {
    $form['submit']['#value'] = t('Register');
  }
}

The user_register form is re-used in the admin section, so any tweaks you make will appear here also. Unusually if you change the submit value, then the admin user register form will break, and bounce you back to admin/user/user without an error message.

All you need to do is make the submit value tweak specific to only the front-end form:

/**
* Implementation of hook_form_alter().
*/
function mymodule_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == 'user_register') {
    if (arg(0) == 'user') {
      $form['submit']['#value'] = t('Register');
    }
  }
}

Et voilĂ !