If you're getting this message:

The type 'System.Data.Linq.DataContext' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. C:\Documents and Settings\pldital\My Documents\Visual Studio 2008\Projects\PatentableServices\Transform\PetabyteCompression.svc.cs 

... add...  System.Data.Linq as a reference to your project.

I still get bit every once in awhile (read: pasting together a poc) when I include a LINQ project in a solution were I've got a dependency !