Urgent Help Needed : WinCC v5.0SP2 vs v5.1

Hi!!
I amNatashaSharmafrom Siemens,India.We have developed our own OPC Client based on OPCDA Specification 2.03 to communicate with third party OPC servers.We have observed that our OPC Client works perfectly with WinCC 5.1.But we have some issues when we try to communicate with WinCC 5.0 SP2. The WinCC project is same for both the cases.In case of WinCC 5.0 SP2 the logical connection between OPC server and OPC client is established.The groups also get added.But when we try to add Items/Tags in these groups in our OPCClient it does not succeed.We want to know whether there is a specification change from WinCC 5.0 SP2 to WinCC 5.1.We also want to know if possible, the changes which are causing the above mentioned problem.We would be grateful if any one can provide us with some information about the same.
You can either reply here or mail me at natasha.sharma@siemens.com
Thanks a lot.