Paypal browser fix

Hi I have had paypal integrated with my website for several years and all was fine. On the 12th November however, some changes must have taken place that is causing cart details to no longer be properly transferred to paypal. The cart still works perfectly in Mac OSX with safari and firefox, but seems to not be working with firefox and internet explorer under windows.? When people click on order button on our server, it communicates with paypal, but then just takes them to the homepage. Works fine in some browsers but not in others. I imagine its just a quick fix with how the site send info to the paypal servers. Interesting the issue doesnt exist with browsers under OSX. Thanks. ## Deliverables Just want the shopping cart to work again in all browsers as it did a week ago. Will pay 50 to commence work, then another 50 once complete. ## Platform Is currently built on php 4 with mysqldatabase on linux.