Oscommerce php 5.3 problems. Need little fix with sessions

Hello, we need an OScommerce specialist able to fix a known problem with the change to php 5.3. We are running an oscommerce with full of contributions and have made the most of changes of the depreciated functions due to the change of php 5.3. Now we do not have any error message any more but there is a session problem (session ID changes with each click and the products do not go into the cart). We will only consider people having experience with oscommerce and having sold those kind of problems. Have a nice day. Kind regards.