Formation pictures within a sequence are not actually stored in the sequence itself, rather the pictures are stored in a separate file. When you changed computers, you may not have copied this file. To restore the pictures, see http://www.ceder.net/faqdb/view.php?section=1&category=34#rec385
See also http://www.ceder.net/faqdb/view.php?section=1&category=5#rec409