Office Addin terminates host while using WCF

It took some time to solve this and the conclusions are interesting.

Our Office (Word/Excel/PowerPoint) add-in sends a request to our custom WCF service, the hosting Office application terminates, leaving this entry in the application log:

Provider: .NET Runtime 
EventID: 1023
Level: 2
Task: 0 
Keywords: 0x80000000000000 
Channel: Application 
EventData: .NET Runtime version 2.0.50727.4200 - Fatal Execution Engine Error (6BC47B3E) (80131506)

To reproduce this, create a new "Word 2007 Add-in" project in Visual Studio 2008. Add references to System.ServiceModel and System.Runtime.Serialization. Modify your ThisAddin class to contain this code, which I believe is the minimum code necessary to reproduce this behaviour:

[Serializable]
public class CustomQuery { }
[Serializable]
public class CustomQueryCollection : ReadOnlyCollection<CustomQuery>
{
    public CustomQueryCollection(IEnumerable<CustomQuery> queries)
        : base(queries.ToArray())
    { }
}
[Serializable]
[KnownType(typeof(CustomQueryCollection))]
public class CustomRequest : ISerializable
{
    readonly CustomQueryCollection _collection;
    public CustomRequest(IEnumerable<CustomQuery> queries)
    {
        _collection = new CustomQueryCollection(queries);
    }
    protected CustomRequest(SerializationInfo info, StreamingContext context)
    {
        _collection = (CustomQueryCollection)info.GetValue("Queries", typeof(CustomQueryCollection));
    }
    public CustomQueryCollection Queries { get { return _collection; } }
    void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("Queries", _collection);
    }
}
[ServiceContract]
public interface ICustomService
{
    [OperationContract]
    void SendRequest(CustomRequest request);
}
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class CustomService : ICustomService
{
    public void SendRequest(CustomRequest request)
    {
        // this line is never reached.
    }
}
public class CustomClient : ClientBase<ICustomService>, ICustomService
{
    public CustomClient(Binding binding, EndpointAddress address)
        : base(binding, address)
    { }
    public void SendRequest(CustomRequest request)
    {
        Channel.SendRequest(request);
    }
}
public partial class ThisAddIn
{
    private void ThisAddIn_Startup(object sender, System.EventArgs e)
    {
        var address = "net.pipe://localhost/kamikaze";
        var endpointAddress = new EndpointAddress(address);
        var binding = new NetNamedPipeBinding();
        using (var serviceHost = new ServiceHost(new CustomService()))
        using (var client = new CustomClient(binding, endpointAddress))
        {
            serviceHost.AddServiceEndpoint(typeof(ICustomService), binding, address);
            serviceHost.Open();
            client.SendRequest(new CustomRequest(new CustomQuery[0]));
            // this line is never reached.
            serivceHost.Close();
        }
    }
    private void ThisAddIn_Shutdown(object sender, System.EventArgs e) { }
    #region VSTO generated code
    private void InternalStartup()
    {
        this.Startup += new System.EventHandler(ThisAddIn_Startup);
        this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);
    }
    #endregion
}

Hit [F5]: Word 2007 starts, and then disappears, leaving the log 开发者_运维技巧message described above in your system's application log. The same code works perfectly fine in all other contexts that we've tried.

Change these lines of code:

[KnownType(typeof(CustomQueryCollection))]
[KnownType(typeof(CustomQuery[]))]

_collection = (CustomQueryCollection)info.GetValue("Queries", typeof(CustomQueryCollection));
_collection = new CustomQueryCollection((CustomQuery[]) info.GetValue("Queries", typeof(CustomQuery[])));

info.AddValue("Queries", _collection);
info.AddValue("Queries", _collection.ToArray());

...there. No more fatal engine execution errors. I suspect this is related to Office being a .Net 2.0 host, while all our other use cases and tests involved .Net 3.5 hosts, but I'm only guessing.