Note that you can also use SQL Server Native Client 10 (the current version) with SQL 2000 and 2005 as well as 2008 - it seems to be the most solid of the drivers. Another thing that hasn't been mentioned is adding a timestamp field to each of the SQL Server tables. Access versions from 2003 forward do that, but the doesn't add the timestamp to all tables. In multi-user situations not having a timestamp can cause errors such as you are seeing. See Using the Upsizing Wizard on the Microsoft Office site for detailed info on upsizing. That said, we always build the tables and relationships in SQL Server, as has been suggested.