How to use linq to sql class in DotNetNuke module?

Question

C++ / C#

OS Windows 8.1 x64. Visual Studio 2012 development environment. Version DotNetNuke 7.3.2.
I am writing a module using linq. I create a project from a template. I am creating a dbml file. It has a Class from a table of the same database that the site itself uses. Then I add a Linq data source to the module page, but I can't select a DataContext object for it. The list of objects is empty.
When I repeat all the same steps in a project created according to the "Empty ASP.NET Web Application" template, then everything works. I can't figure out what the difference is.