Question of datasources in vwd 2008 express

set up a new web according to sample at

http://msdn.microsoft.com/zh-cn/library/ms165732(SQL.100).aspx

I use database AdventureWorksLT2008R2_Data.mdf which is work well in SQLExpress. when I config datasources in vwd 2008 express. I get

prompt of error of query: no object Product,

what's matter?