fix for: http://drupal.org/node/300084?page=1#comment-3089288

diff -Nurp ../cck.orig/modules/fieldgroup/fieldgroup.module ./modules/fieldgroup/fieldgroup.module
--- ../cck.orig/modules/fieldgroup/fieldgroup.module	2010-06-15 09:18:54.000000000 -0500
+++ ./modules/fieldgroup/fieldgroup.module	2010-06-15 09:45:42.000000000 -0500
@@ -223,9 +223,9 @@ function fieldgroup_remove_group_submit(
   $form_values = $form_state['values'];
   $content_type = $form['#content_type'];
   $group_name = $form['#group_name'];
-  $parent_group_name = db_fetch_array(db_query("SELECT parent_group_name FROM {". fieldgroup_tablename() ."} WHERE group_name = '%s' and type_name = '%s'", $group_name, $content_type['type']));
-  $result = db_query("UPDATE {". fieldgroup_tablename() ."} SET parent_group_name = '%s' WHERE parent_group_name = '%s'", $parent_group_name['parent_group_name'], $group_name);
-  $result = db_query("UPDATE {". fieldgroup_fields_tablename() ."} SET group_name = '%s' WHERE group_name = '%s'", $parent_group_name['parent_group_name'], $group_name);
+  $parent_group_name = db_fetch_array(db_query("SELECT parent_group_name FROM {". fieldgroup_tablename() ."} WHERE group_name = '%s' AND type_name = '%s'", $group_name, $content_type['type']));
+  $result = db_query("UPDATE {". fieldgroup_tablename() ."} SET parent_group_name = '%s' WHERE parent_group_name = '%s' AND type_name = '%s'", $parent_group_name['parent_group_name'], $group_name, $content_type['type']);
+  $result = db_query("UPDATE {". fieldgroup_fields_tablename() ."} SET group_name = '%s' WHERE group_name = '%s' AND type_name = '%s'", $parent_group_name['parent_group_name'], $group_name, $content_type['type']);
   fieldgroup_delete($content_type['type'], $group_name);
   drupal_set_message(t('The group %group_name has been removed.', array('%group_name' => $group_name)));
   $form_state['redirect'] = 'admin/content/node-type/'. $content_type['url_str'] .'/fields';