SQLServer via LinqToSQL + Silverlight 2

[Cololi]

Hi,

I'm working with Visual Studio 2008, C# (FrameWork 3.5), Silverlight 2 and
SQL Server 2005.

I'm trying to display data from this database in a "DataGrid" (Silverlight 2
component)
LinqToSQL created classes well.
Then I created a WCF service in order to link the Silverlight module and the
database.

The problem :
When I create a function in the service that return List <string> that works
well.
But if I want to return List<MyTableName> Silverlight can't see the result.

I already changed the serrialization of classes made by LINQToSQL to
Unidirectionnal.
But it doesn't work ...

What should I do ?

Thanks.