Hi Dave,
How many data sources do you have? Are you setting the values from within the main data source or are you setting from a secondary data source? Office 2007 has a cool new logic inspector that will help debug these issues, but it's only released in beta. We could look at the form for you. Check out About Us and fill out the Submit Project Inquiry page for more info.
Patrick Halstead
Project Manager at Qdabra