If you need to debug a Silverlight project that references a RIA Service project that host the Entity Framework mapping with the Data Access Layer logic, you need to insert inside the App.config file in the RIA Service this xml node
<system.web> <compilation debug="true" strict="false" explicit="true" targetFramework="4.0" /> <httpModules> <add name="DomainServiceModule" type="System.ServiceModel.DomainServices.Hosting.DomainServiceHttpModule, System.ServiceModel.DomainServices.Hosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> </httpModules> </system.web>