简单的 VB 到 C# 和 Web 服务错误

我有一个简单的Web服务方法，我正在尝试转换：

<WebMethod()> _
<ScriptMethod(ResponseFormat:=ResponseFormat.Json, UseHttpGet:=True)> _
Public Function GetEmployees() As Object
    Dim _db As New DataClasses1DataContext()
    Return New With {.data = _db.Employees}
End Function

这是我的 C# 代码：

[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json, UseHttpGet = true)]
public object GetEmployees()
{
    DBModelDataContext _db = new DBModelDataContext();
    return new { data = _db.Employees };
}

但是当我运行我的服务时，我收到一个错误：

System.InvalidOperationException: Wystąpił błąd podczas generowania dokumentu XML. --->
System.InvalidOperationException: Aby serializacja XML była możliwa, dla typów dziedziczących po elemencie IEnumerable należy zaimplementować metodę Add(System.Object) na wszystkich poziomach hierarchii dziedziczenia. Dla elementu System.Data.Linq.Table`1[[Scheduler.db.Employee, Scheduler, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] metoda Add(System.Object) nie jest implementowana.
w System.Xml.Serialization.TypeScope.GetEnumeratorElementType(Type type, TypeFlags& flags)
w System.Xml.Serialization.TypeScope.ImportTypeDesc(Type type, MemberInfo memberInfo, Boolean directReference)
w System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throwOnError)
w System.Xml.Serialization.XmlSerializationWriter.CreateUnknownTypeException(Type type)
w System.Xml.Serialization.XmlSerializationWriter.WriteTypedPrimitive(String name, String ns, Object o, Boolean xsiType)
w Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write1_Object(String n, String ns, Object o, Boolean isNullable, Boolean needType)
w Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write2_anyType(Object o)
w Microsoft.Xml.Serialization.GeneratedAssembly.ObjectSerializer.Serialize(Object objectToSerialize, XmlSerializationWriter writer)
w System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)
--- Koniec śladu stosu wyjątków wewnętrznych ---
w System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)
w System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o, XmlSerializerNamespaces namespaces)
w System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o)
w System.Web.Services.Protocols.XmlReturnWriter.Write(HttpResponse response, Stream outputStream, Object returnValue)
w System.Web.Services.Protocols.HttpServerProtocol.WriteReturns(Object[] returnValues, Stream outputStream)
w System.Web.Services.Protocols.WebServiceHandler.WriteReturns(Object[] returnValues)
w System.Web.Services.Protocols.WebServiceHandler.Invoke()

我现在被这个困住了 4 个小时：/

我有一个简单的sql服务器数据库，其中包含2个表员工和计划。

我需要这种格式来与 Ext 调度程序一起使用。VB代码来自Ext Scheduler网页上的演示，我只想将其转换为C#。

编辑：我使用的是Visual Studio 2008（.NET 3.5），VB中的演示是在2010年（.NET 4.0）中创建的。