includes/usercp_activate.php

FIND:

		if (intval($board_config['require_activation']) == USER_ACTIVATION_ADMIN && $userdata['user_level'] != ADMIN)
		{
			message_die(GENERAL_MESSAGE, $lang['Not_Authorised']);
		}

REPLACE WITH:

		if (intval($board_config['require_activation']) == USER_ACTIVATION_ADMIN && $row['user_newpasswd'] == '')
		{
			if (!$userdata['session_logged_in'])
			{
				redirect(append_sid('login.' . $phpEx . '?redirect=profile.' . $phpEx . '&mode=activate&' . POST_USERS_URL . '=' . $row['user_id'] . '&act_key=' . trim($HTTP_GET_VARS['act_key'])));
			}
			else if ($userdata['user_level'] != ADMIN)
			{
				message_die(GENERAL_MESSAGE, $lang['Not_Authorised']);
			}
		}