ADO.NET Data Services with EF implementing table per concrete type (TPCT) inheritance

Question

I am working with a SQL data source that has duplicate data in multiple tables. I have no control over the database. For my project, I've created an EF model and an ADO.NET data service (using VS 2008) that exposes it. I also have a .NET client application that consumes the service.

Now, these db tables have a large number of fields common, which I need to hydrate in my client before sending an insert request to the service. So, wanting to avoid repetitive code, I created an abstract base class in my EF model and put all the common properties in it. The entity set name of this base class is OrderEntries. One of the entities inheriting from it is called OEORDH. It maps to a db table. To expose this entity, I created a WebGet service method because the query uses OfType method, which has no supported translation to ATOM; hence I can't use it in my client. Here's the method:

<WebGet()> _
Public Function Orders() As IQueryable(Of OEORDH)
    Dim results = From x In Me.CurrentDataSource.OrderEntries.OfType(Of OEORDH)()
    Return results
End Function

When I access this method in the browser (http://localhost:1187/MyService.svc/Orders), I get a very generic error back:

<link rel="self" title="Orders" href="Orders" />
  <m:error>
    <m:code></m:code>
    <m:message xml:lang="en-US">An error occurred while processing this request.</m:message>
  </m:error>

But I know that the query gets called, and moreover, when I watch the Locals window in debug, I see that it returns the right collection of objects. Other web methods that query non-inheriting entities work just fine. What is wrong?

UPDATE I followed Steve's advice and set IncludeExceptionDetailInFaults to true. I also set UseVerboseErrors to true. The trace log now shows that the exception being thrown is System.ServiceModel.CommunicationObjectAbortedException, which is still pretty generic. I searched the web, but didn't find anything concrete. The message is: The communication object, System.ServiceModel.Channels.TransportReplyChannelAcceptor+TransportReplyChannel, cannot be used for communication because it has been Aborted. Here's the stack content:

System.ServiceModel.Channels.CommunicationObject.ThrowIfAborted()
System.ServiceModel.Channels.InputQueueChannel`1.EndDequeue(IAsyncResult result, TDisposable& item)
System.ServiceModel.Channels.ReplyChannel.EndTryReceiveRequest(IAsyncResult result, RequestContext& context)
System.ServiceModel.Dispatcher.ReplyChannelBinder.EndTryReceive(IAsyncResult result, RequestContext& requestContext)
System.ServiceModel.Dispatcher.ErrorHandlingReceiver.EndTryReceive(IAsyncResult result, RequestContext& requestContext)
System.ServiceModel.Dispatcher.ChannelHandler.AsyncMessagePump(IAsyncResult result)
System.ServiceModel.Dispatcher.ChannelHandler.OnAsyncReceiveComplete(IAsyncResult result)
System.ServiceModel.Diagnostics.Utility.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
System.ServiceModel.AsyncResult.Complete(Boolean completedSynchronously)
System.ServiceModel.Channels.InputQueue`1.AsyncQueueReader.Set(Item item)
System.ServiceModel.Channels.InputQueue`1.Shutdown(CommunicationObject communicationObject)
System.ServiceModel.Channels.InputQueueChannel`1.OnClosing()
System.ServiceModel.Channels.CommunicationObject.Abort()
System.ServiceModel.Dispatcher.ReplyChannelBinder.Abort()
System.ServiceModel.Channels.ServiceChannel.OnAbort()
System.ServiceModel.Channels.CommunicationObject.Abort()
System.Data.Services.DelegateBodyWriter.OnWriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.BodyWriter.WriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.BodyWriterMessage.OnWriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.Message.OnWriteMessage(XmlDictionaryWriter writer)
System.ServiceModel.Channels.Message.WriteMessage(XmlDictionaryWriter writer)
System.ServiceModel.Channels.HttpStreamMessageEncoderFactory.HttpStreamMessageEncoder.WriteMessage(Message message, Stream stream)
System.ServiceModel.Channels.HttpStreamMessageEncoderFactory.HttpStreamMessageEncoder.WriteMessage(Message message, Int32 maxMessageSize, BufferManager bufferManager, Int32 messageOffset)
System.ServiceModel.Channels.WebMessageEncoderFactory.WebMessageEncoder.WriteMessage(Message message, Int32 maxMessageSize, BufferManager bufferManager, Int32 messageOffset)
System.ServiceModel.Channels.HttpOutput.SerializeBufferedMessage(Message message)
System.ServiceModel.Channels.HttpOutput.Send(TimeSpan timeout)
System.ServiceModel.Channels.HttpRequestContext.OnReply(Message message, TimeSpan timeout)
System.ServiceModel.Activation.HostedHttpContext.OnReply(Message message, TimeSpan timeout)
System.ServiceModel.Channels.RequestContextBase.Reply(Message message, TimeSpan timeout)
System.ServiceModel.Channels.RequestContextBase.Reply(Message message)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.Reply(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessageCleanup(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc& rpc)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc& rpc)
System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)
System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.Dispatch(MessageRpc& rpc, Boolean isOperationContextSet)
System.ServiceModel.Dispatcher.ChannelHandler.DispatchAndReleasePump(RequestContext request, Boolean cleanThread, OperationContext currentOperationContext)
System.ServiceModel.Dispatcher.ChannelHandler.HandleRequest(RequestContext request, OperationContext currentOperationContext)
System.ServiceModel.Dispatcher.ChannelHandler.AsyncMessagePump(IAsyncResult result)
System.ServiceModel.Dispatcher.ChannelHandler.OnAsyncReceiveComplete(IAsyncResult result)
System.ServiceModel.Diagnostics.Utility.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
System.ServiceModel.AsyncResult.Complete(Boolean completedSynchronously)
System.ServiceModel.Channels.InputQueue`1.AsyncQueueReader.Set(Item item)
System.ServiceModel.Channels.InputQueue`1.EnqueueAndDispatch(Item item, Boolean canDispatchOnThisThread)
System.ServiceModel.Channels.InputQueue`1.EnqueueAndDispatch(T item, ItemDequeuedCallback dequeuedCallback, Boolean canDispatchOnThisThread)
System.ServiceModel.Channels.InputQueueChannel`1.EnqueueAndDispatch(TDisposable item, ItemDequeuedCallback dequeuedCallback, Boolean canDispatchOnThisThread)
System.ServiceModel.Channels.SingletonChannelAcceptor`3.Enqueue(QueueItemType item, ItemDequeuedCallback dequeuedCallback, Boolean canDispatchOnThisThread)
System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, ItemDequeuedCallback callback)
System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result)
System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest()
System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest()
System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state)
System.ServiceModel.PartialTrustHelpers.PartialTrustInvoke(ContextCallback callback, Object state)
System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequestWithFlow(Object state)
System.ServiceModel.Channels.IOThreadScheduler.CriticalHelper.WorkItem.Invoke2()
System.ServiceModel.Channels.IOThreadScheduler.CriticalHelper.WorkItem.Invoke()
System.ServiceModel.Channels.IOThreadScheduler.CriticalHelper.ProcessCallbacks()
System.ServiceModel.Channels.IOThreadScheduler.CriticalHelper.CompletionCallback(Object state)
System.ServiceModel.Channels.IOThreadScheduler.CriticalHelper.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
System.ServiceModel.Diagnostics.Utility.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped)
System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)