Problems with merge replication

Question

Hi,

We are developing a multi-user desktop application with users located in different countries. The platform is - .net 3.5, SQL Server 2008, WinForms. Now, my client has used the help of a DBA who has implemented merge replication. To facilitate replication, we made all our primary keys as GUID. Now, we are facing these issues with replication -

subscribers expiration sometimes stops replication and we have found no clean way to re-add

every change to db schema requires to poll the whole data all over again! This seems to be strange, what could be the problem here?

Also, sometimes we have duplicate keys, and that too stops replication

I am sure these issues can be resolved. Maybe, we have not gone the right way to implement. Can you suggest how to go about implementing. Or, is the above information enough to diagnose the problem?