Need Urgent Quick Oscommerce Fix

I have SPPC 4.2 (separate prices per customer) contrib installed and it's working everywhere except on [login to view URL] - as soon as I procceed through checkout and get to this page it displays the retail price rather than the new trade price and as a result the wrong price is used for the order total. Think the problem might be with one of the class files. Needs fixing asap, please dont bid unless you can do it now. Heavily modified site so no amateurs please. Could be a 10 minute job for the right person. Another option is to go through the full installation again and check if anything is missing. Thanks