I've created a small Prism application (using MEF) with the following parts: - Infrastructure project, that contains a global file of region names. - Main project, that has 2 buttons to load other modules. - ModulesInterfaces project, where I've defined an IDataAccess interface for my DataAccess module. - DataAccess project, where there are several files but one main DataAccess class that implements both IDataAccess and IModule. When the user click a button, I want to show him a list of employees, so I need the DataAccess module. My code is as follows: var namesView = new EmployeesListView(); var namesViewModel = new EmployeesListViewModel(employeeRepository); namesView.DataContext = namesViewModel; namesViewModel.EmployeeSelected += EmployeeSelected; LocateManager(); manager.Regions["ContentRegion"].Add(new NoEmployeeView(), "noEmployee"); manager.Regions["NavigationRegion"].Add(namesView); I get an exception in my code when I'm trying to get DataAccess as a service (via ServiceLocator). I'm not sure if that's the right way to go, but trying to get it from the ModuleCatalog (as a type IDataAccess returns an empty enumeration). I'd appreciate some directions. Thanks. The problematic code line: object instance = ServiceLocator.Current.GetInstance(typeof(DataAccess.DataAccess)); The exact exception: Activation error occured while trying to get instance of type DataAccess, key "" The inner exception is null, the stack trace: at Microsoft.Practices.Prism.MefExtensions.MefServiceLocatorAdapter.DoGetInstance(Type serviceType, String key) in c:\release\WorkingDir\PrismLibraryBuild\PrismLibrary\Desktop\Prism.MefExtensions\MefServiceLocatorAdapter.cs:line 76 at Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstance(Type serviceType, String key) Edit The same exception is thrown for: container = (CompositionContainer)ServiceLocator.Current.GetInstance(typeof(CompositionContainer));