Correct Shipping Rate Post in Existing Shopping Cart / Check Out

I have a website for a client of mine that has a cart that was custom designed but for which I cannot make contact with the person that designed it. It uses only USPS to get its shipping calculations. Everything in general is working fine and it only offers priority or parcel. Was working fine until about a month ago when it started to show only the periority rate and not the parcel. I really do not know where to start looking in the code to correct this. Also do not know if this problem has anything with the US post office changing their rates about the time the problem started. If a USPS parcel rate can no longer be retrieved, we may be able to accept the two lowest UPS rates. I have a USPS account number for you if needed. See attached file for instructions to view problem. Also note that every other aspect of calculation and process works fine. Shipping is calculated by using source zip, destination zip, total weight and a packaging add on. I do not know exactly where any of this code is located. I will give FTP access information along with back end information after bid has been accepted. I can communicate by Skype or email to assist best I can. All files updated need be backed up first. MAX BID = $30.00 US