Here's some info I found helpful in debugging odata.

http://blogs.msdn.com/b/phaniraj/archive/2008/06/18/debugging-ado-net-data-services.aspx

With this debugging turned on, I get the following, actually helpful, debug info:

The server encountered an error processing the request. The exception message is 'The property 'Errors' on type 'DomainModel.User' is not a valid property. Make sure that the type of the property is a public type and a supported primitive type or a entity type with a valid key or a complex type.'. See server logs for more details. The exception stack trace is:

at System.Data.Services.Providers.ReflectionServiceProvider.BuildTypeProperties(ResourceType parentResourceType, IDictionary`2 knownTypes, IDictionary`2 childTypes, Queue`1 unvisitedTypes, IEnumerable`1 entitySets) at System.Data.Services.Providers.ReflectionServiceProvider.PopulateMetadataForTypes(IDictionary`2 knownTypes, IDictionary`2 childTypes, Queue`1 unvisitedTypes, IEnumerable`1 entitySets) at System.Data.Services.Providers.ReflectionServiceProvider.PopulateMetadata(IDictionary`2 knownTypes, IDictionary`2 childTypes, IDictionary`2 entitySets) at System.Data.Services.Providers.BaseServiceProvider.PopulateMetadata() at System.Data.Services.DataService`1.CreateProvider() at System.Data.Services.DataService`1.HandleRequest() at System.Data.Services.DataService`1.ProcessRequestForMessage(Stream messageBody) at SyncInvokeProcessRequestForMessage(Object , Object[] , Object[] ) at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage41(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage11(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)

    [TestClass]
    public class ODataCRUDTests
    {
        public ODataCRUDTests()
        {
            context = new NorthwindIBEntities(new Uri("http://localhost:9009/MyData.svc"));
        }
 
        private TestContext testContextInstance;
 
        /// <summary>
        ///Gets or sets the test context which provides
        ///information about and functionality for the current test run.
        ///</summary>
        public TestContext TestContext
        {
            get
            {
                return testContextInstance;
            }
            set
            {
                testContextInstance = value;
            }
        }
 
        #region Additional test attributes
        //
        // You can use the following additional attributes as you write your tests:
        //
        // Use ClassInitialize to run code before running the first test in the class
        // [ClassInitialize()]
        // public static void MyClassInitialize(TestContext testContext) { }
        //
        // Use ClassCleanup to run code after all tests in a class have run
        // [ClassCleanup()]
        // public static void MyClassCleanup() { }
        //
        // Use TestInitialize to run code before running each test 
        // [TestInitialize()]
        // public void MyTestInitialize() { }
        //
        // Use TestCleanup to run code after each test has run
        // [TestCleanup()]
        // public void MyTestCleanup() { }
        //
        #endregion
 
        [TestMethod]
        public void then_can_get_Customers()
        {
            var customers = context.Customers.ToList();
 
            Assert.IsTrue(customers.Any(), "Should have some customers");
        }
 
        [TestMethod]
        public void then_can_get_Customer_Orders()
        {
            var customer = context.Customers.First();
            Assert.IsTrue(customer != null, "We should have a customer");
 
            context.LoadProperty(customer, "Orders");
            Assert.IsTrue(customer.Orders.Any(), "We should have orders");
        }
 
        [TestMethod]
        public void then_can_modify_Customer()
        {
            var customer1 = context.Customers.First();
            string newRegion = Guid.NewGuid().ToString().Substring(0, 15);
 
            customer1.Region = newRegion;
 
            context.UpdateObject(customer1);
            context.SaveChanges();
 
            var query = from c in context.Customers
                        where c.CustomerID == customer1.CustomerID
                        select c;
 
            var customer2 = query.FirstOrDefault();
 
            Assert.IsTrue(customer2 != null && customer2.Region == newRegion, "Customer should have been updated");
        }
 
        [TestMethod]
        public void then_can_add_Customer()
        {
            Customer customer = Customer.CreateCustomer(Guid.NewGuid());
 
            string companyName = Guid.NewGuid().ToString();
            customer.CompanyName = companyName;
 
            context.AddToCustomers(customer);
            context.SaveChanges();
 
            Assert.IsTrue(context.Customers.Where(c => c.CompanyName == companyName).ToList().Any(),
                          "The new customer should have been added");
        }
 
        [TestMethod]
        public void then_can_delete_Customer()
        {
            var customers = (from c in context.Customers
                             where c.CustomerID_OLD == null
                             select c).ToList();
 
            Assert.IsTrue(customers.Any(), "No customers to delete. Please add a test customer first");
 
            context.DeleteObject(customers.First());
            context.SaveChanges();
 
            var customers2 = (from c in context.Customers
                              where c.CustomerID_OLD == null
                              select c).ToList();
 
            Assert.IsTrue(customers2.Count == customers.Count - 1, "We should have one less customers");
        }
 
        [TestMethod]
        public void then_can_add_new_Order_to_Customer()
        {
            var customer = context.Customers.FirstOrDefault();
            Assert.IsTrue(customer != null, "Should have a customer");
 
            context.LoadProperty(customer, "Orders");
            var numberOfOrders = customer.Orders.Count();
 
            var shippingAddress = new ShippingAddress();
            shippingAddress.ShipAddress = "111";
            shippingAddress.ShipCity = "Emeryville";
            shippingAddress.ShipPostalCode = "11111";
 
            var order = Order.CreateOrder(-1, 1, shippingAddress);
            context.AddRelatedObject(customer, "Orders", order);
            context.SaveChanges();
 
            context.LoadProperty(customer, "Orders");
            Assert.IsTrue(customer.Orders.Count() == numberOfOrders + 1, "This customer should have one more order");
        }
 
        [TestMethod]
        public void then_can_support_calculated_Properties_in_partial_Entity_Class()
        {
            var customer = context.Customers.FirstOrDefault();
 
            Assert.IsTrue(customer.TestCalculatedProperty == "Test", "Calculated property should be set");
        }
 
        [TestMethod]
        public void then_can_set_Employee_Birthday_to_null()
        {
            var employee = context.Employees.Where(e => e.BirthDate != null).First();
            Assert.IsNotNull(employee, "We need an employee with a BirthDate");
 
            employee.BirthDate = null;
 
            context.UpdateObject(employee);
            context.SaveChanges();
 
            var query = from e in context.Employees
                        where e.EmployeeID == employee.EmployeeID
                        select e;
 
            var employee2 = query.FirstOrDefault();
            Assert.IsNull(employee2.BirthDate, "Birthdate should be null");
        }
 
        private NorthwindIBEntities context;
    }
}

    public class MyData : DataService<NorthwindIBEntities>
    {
        // This method is called only once to initialize service-wide policies.
        public static void InitializeService(DataServiceConfiguration config)
        {
            config.UseVerboseErrors = true;
            // TODO: set rules to indicate which entity sets and service operations are visible, updatable, etc.
            config.SetEntitySetAccessRule("Customers", EntitySetRights.All);
            config.SetEntitySetAccessRule("Orders", EntitySetRights.All);
            config.SetEntitySetAccessRule("Employees", EntitySetRights.All);
 
            config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;
        }
    }
}