diff -urp date-original/date/date_repeat.inc date/date/date_repeat.inc
--- date-original/date/date_repeat.inc	2009-02-21 06:53:25.000000000 -0600
+++ date/date/date_repeat.inc	2009-03-26 17:49:06.000000000 -0500
@@ -76,7 +76,11 @@ function _date_repeat_widget_validate($e
   if (empty($values['UNTIL']['datetime'])) {
     form_set_error($error_field, t('The UNTIL value is required for repeating dates.'));
   }
+  
+  // If errors have been set, clean up the form and return.
   if (form_get_errors()) {
+    $form_values[$field_name]['rrule'] = NULL;
+    form_set_value($element, array($form_values[$field_name]), $form_state);
     return;
   }
 
diff -urp date-original/date_api_ical.inc date/date_api_ical.inc
--- date-original/date_api_ical.inc	2009-02-21 06:53:25.000000000 -0600
+++ date/date_api_ical.inc	2009-03-26 17:28:05.000000000 -0500
@@ -649,7 +649,8 @@ function date_api_ical_build_rrule($form
     $RRULE .= ';BYMONTHDAY='. $BYMONTHDAY;
   }
   // The UNTIL date is supposed to always be expressed in UTC.
-  if (array_key_exists('UNTIL', $form_values) && array_key_exists('datetime', $form_values['UNTIL'])) {
+  // Do not add an UNTIL value if it's NULL 
+  if (array_key_exists('UNTIL', $form_values) && array_key_exists('datetime', $form_values['UNTIL']) && $form_values['UNTIL']['datetime'] != NULL) {
     $until = date_ical_date($form_values['UNTIL'], 'UTC');
     $RRULE .= ';UNTIL='. date_format($until, DATE_FORMAT_ICAL) .'Z';
   }