When trying to edit a term, the AHAH request to retrieve the edit for comes back with this error: 500 (Service unavailable (with message)). The error is occurring in some server environments, but not others. Fortunately, the fix is quite simple. A NULL $form_state variable is being passed to drupal_prepare_form(). Setting the
$form_state variable to
array('submitted' => FALSE) fixes the problem. I've attached a patch.