I'm getting the following error in my MVC2 app using Linq to SQL (I am new to both). I am connected to an actual SQL server not weird mdf:

System.InvalidOperationException The null value cannot be assigned to a member with type System.Int64 which is a non-nullable value type

My SQL table has a column called MessageID. It is BigInt type and has a primary key, NOT NULL and an IDENTITY 1 1, no Default

In my dbml designer it has the following declaration for this field:

[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_MessageId", AutoSync=AutoSync.OnInsert, DbType="BigInt NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
public long MessageId
{
    get
    {
        return this._MessageId;
    }
    set
    {
        if ((this._MessageId != value))
        {
            this.OnMessageIdChanging(value);
            this.SendPropertyChanging();
            this._MessageId = value;
            this.SendPropertyChanged("MessageId");
            this.OnMessageIdChanged();
        }
    }
}

It keeps telling me that null cannot be assigned - I'm not passing through null! It's a long - it can't even be null!

Am I doing something stupid? I can't find a solution anywhere!

I made this work by changing the type of this property to Nullable<long> but surely this can't be right?

Update: I am using InsertOnSubmit. Simplified code:

public ActionResult Create(Message message)
{
    if (ModelState.IsValid)
    {
       var db = new MessagingDataContext();
       db.Messages.InsertOnSubmit(message);
       db.SubmitChanges(); //line 93 (where it breaks)
    }
}

breaks on SubmitChanges() with the error at the top of this question.

Update2: Stack trace:

   at Read_Object(ObjectMaterializer`1 )
   at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()
   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
   at System.Data.Linq.ChangeDirector.StandardChangeDirector.DynamicInsert(TrackedObject item)
   at System.Data.Linq.ChangeDirector.StandardChangeDirector.Insert(TrackedObject item)
   at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode)
   at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode)
   at Qanda.Controllers.MessagingController.Ask(Message message) in C:\Qanda\Qanda\Controllers\MessagingController.cs:line 93

Update3: No one knows and I don't have enough clout to offer a bounty! So continued on my ASP.NET blog. Please help!