Sterling serialization problem on Windows Phone 7

I have a problem with Sterling Database for Windows Phone. I implemented the database step by step in my wp7app, but it doesn't serialize my data when new entities are save开发者_开发问答d. For example: I serialize credentials using sterling database:

        var userCredentials = new UserCredentials(userName, password);
        App.Database.Save(userCredentials);
        App.Database.Flush();

But when the application is reactivated (or re-launched) Sterling doesn't return any values from isolated storage:

var firstOrDefault = App.Database.Query<UserCredentials, string>()
            .ToList()
            .FirstOrDefault();

My ActivateEngine method looks are standard and TableDefinition is:

CreateTableDefinition< UserCredentials, string >(t => t.UserName),

Why is sterling database doesn't serialize my data? Everything seems to be implemented fine. Please help.

Are you activating and registering the database on startup and diposing on completion as described in the Quickstart?

My personal preference is to use an application service similar to the following:

namespace MyApp.Data
{
    using System.Windows;
    using Wintellect.Sterling;
    using Wintellect.Sterling.IsolatedStorage;

    /// 
    /// Defines a an application service that supports the Sterling database.
    /// 
    public class SterlingDatabaseService : IApplicationService, IApplicationLifetimeAware
    {
        public static SterlingDatabaseService Current { get; private set; }

        public ISterlingDatabaseInstance Database { get; private set; }

        private SterlingEngine _engine;

        /// 
        /// Called by an application in order to initialize the application extension service.
        /// 
        /// Provides information about the application state.
        public void StartService(ApplicationServiceContext context)
        {
            Current = this;
            _engine = new SterlingEngine();
        }

        /// 
        /// Called by an application in order to stop the application extension service.
        /// 
        public void StopService()
        {
            _engine = null;
        }

        /// 
        /// Called by an application immediately before the  event occurs.
        /// 
        public void Starting()
        {
            _engine.Activate();
            Database = _engine
                .SterlingDatabase
                .RegisterDatabase(new IsolatedStorageDriver());
        }

        /// 
        /// Called by an application immediately after the  event occurs.
        /// 
        public void Started()
        {
            return;
        }

        /// 
        /// Called by an application immediately before the  event occurs.
        /// 
        public void Exiting()
        {
            _engine.Dispose();
        }

        /// 
        /// Called by an application immediately after the  event occurs.
        /// 
        public void Exited()
        {
            return;
        }
    }
}

If you use this approach, don't forget to add an instance in App.xaml:

    <Application.ApplicationLifetimeObjects>
        <!-- Required object that handles lifetime events for the application. -->
        <shell:PhoneApplicationService Activated="Application_Activated"
                                       Closing="Application_Closing"
                                       Deactivated="Application_Deactivated"
                                       Launching="Application_Launching" />
        <data:SterlingDatabaseService />
    </Application.ApplicationLifetimeObjects>