Figure 1. Add a System.Query Reference to Your DLinq Project When you add your first DLinqClass object to the DLinq and press F5 to build and run the project, you might receive this error: "Reference required to assembly 'System.Query, Version=1.0.2319.19041, Culture=neutral, PublicKeyToken=null' containing the implemented interface 'System.Query.IQueryable`1'. Add one to your project." If you incur the build error, add the reference as shown here.