C# 尝试更新服务引用时出现异常！

我有一个Silverlight应用程序，它使用Web服务来支持Multitporpose， 当我看到这些标记时：

[XmlInclude(typeof(StringCustomField))]

在我的一节课上，我遇到了这样的错误：

System.InvalidOperationException: An exception was thrown in a call to a WSDL export extension: System.ServiceModel.Description.DataContractSerializerOperationBehavior
 contract: SCI4WebService ----> **System.IO.FileNotFoundException: Could not load file or assembly 'System.Xml**, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or one of its dependencies. O sistema não pode encontrar o arquivo especificado.
   at System.ModuleHandle.ResolveType(Int32 typeToken, RuntimeTypeHandle* typeInstArgs, Int32 typeInstCount, RuntimeTypeHandle* methodInstArgs, Int32 methodInstCount)
   at System.ModuleHandle.ResolveTypeHandle(Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)
   at System.Reflection.Module.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)
   at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, Module decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, RuntimeMethodHandle& ctor, Boolean& ctorHasParameters, Boolean& isVarArg)
   at System.Reflection.CustomAttribute.GetCustomAttributes(Module decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes)
   at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeType type, RuntimeType caType, Boolean inherit)
   at System.RuntimeType.GetCustomAttributes(Type attributeType, Boolean inherit)
   at System.Runtime.Serialization.DataContract.TryGetDCAttribute(Type type, DataContractAttribute& dataContractAttribute)
   at System.Runtime.Serialization.DataContract.GetStableName(Type type, Boolean& hasDataContract)
   at System.Runtime.Serialization.DataContract.GetCollectionStableName(Type type, Type itemType, CollectionDataContractAttribute& collectionContractAttribute)
   at System.Runtime.Serialization.CollectionDataContract.CollectionDataContractCriticalHelper..ctor(Type type, CollectionKind kind, Type itemType, MethodInfo getEnumeratorMethod, MethodInfo addMethod, ConstructorInfo constructor)
   at System.Runtime.Serialization.CollectionDataContract.IsCollectionOrTryCreate(Type type, Boolean tryCreate, DataContract& dataContract, Type& itemType, Boolean constructorRequired)
   at System.Runtime.Serialization.CollectionDataContract.TryCreate(Type type, DataContract& dataContract)
   at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type)
   at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type)
   at System.Runtime.Serialization.DataContract.GetDataContract(RuntimeTypeHandle typeHandle, Type type, SerializationMode mode)
   at System.Runtime.Serialization.DataContractSet.GetDataContract(Type clrType)
   at System.Runtime.Serialization.DataContractSet.GetMemberTypeDataContract(DataMember dataMember)
   at System.Runtime.Serialization.DataContractSet.AddClassDataContract(ClassDataContract classDataContract)
   at System.Runtime.Serialization.DataContractSet.Add(XmlQualifiedName name, DataContract dataContract)
   at System.Runtime.Serialization.DataContractSet.AddCollectionDataContract(CollectionDataContract collectionDataContract)
   at System.Runtime.Serialization.DataContractSet.Add(XmlQualifiedName name, DataContract dataContract)
   at System.Runtime.Serialization.DataContractSet.AddClassDataContract(ClassDataContract classDataContract)
   at System.Runtime.Serialization.DataContractSet.Add(XmlQualifiedName name, DataContract dataContract)
   at System.Runtime.Serialization.DataContractSet.AddCollectionDataContract(CollectionDataContract collectionDataContract)
   at System.Runtime.Serialization.DataContractSet.Add(XmlQualifiedName name, DataContract dataContract)
   at System.Runtime.Serialization.DataContractSet.AddClassDataContract(ClassDataContract classDataContract)
   at System.Runtime.Serialization.DataContractSet.Add(XmlQualifiedName name, DataContract dataContract)
   at System.Runtime.Serialization.DataContractSet.Add(Type type)
   at System.Runtime.Serialization.XsdDataContractExporter.Export(Type type)
   at System.ServiceModel.Description.MessageContractExporter.ExportType(Type type, String partName, String operationName, XmlSchemaType& xsdType)
   at System.ServiceModel.Description.DataContractSerializerMessageContractExporter.ExportBody(Int32 messageIndex, Object state)
   at System.ServiceModel.Description.MessageContractExporter.ExportMessage(Int32 messageIndex, Object state)
   at System.ServiceModel.Description.MessageContractExporter.ExportMessageContract()
   at System.ServiceModel.Description.DataContractSerializerOperationBehavior.System.ServiceModel.Description.IWsdlExportExtension.ExportContract(WsdlExporter exporter, WsdlContractConversionContext contractContext)
   at System.ServiceModel.Description.WsdlExporter.CallExtension(WsdlContractConversionContext contractContext, IWsdlExportExtension extension)
   --- End of inner ExceptionDetail stack trace ---
   at System.ServiceModel.Description.ServiceMetadataBehavior.MetadataExtensionInitializer.GenerateMetadata()
   at System.ServiceModel.Description.ServiceMetadataExtension.EnsureInitialized()
   at System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.InitializationData.InitializeFrom(ServiceMetadataExtension extension)
   at System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.GetInitData()
   at System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.TryHandleDocumentationRequest(Message httpGetRequest, String[] queries, Message& replyMessage)
   at System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.ProcessHttpRequest(Message httpGetRequest)
   at System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.Get(Message message)
   at SyncInvokeGet(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.ProcessMessage4(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)</PRE></DIV></BODY></HTML>
--.
Metadata contains a reference that cannot be resolved: 'http://localhost:1071/SCI4WebService.svc'.
Content Type application/soap+xml; charset=utf-8 was not supported by service http://localhost:1071/SCI4WebService.svc.  The client and service bindings may be mismatched.
The remote server returned an error: (415) Unsupported Media Type.
If the service is defined in the current solution, try building the solution and adding the service reference again.

System.InvalidOperationException:调用WSDL导出扩展时引发异常：System.ServiceModel.Description.DataContractSerializeRopection行为
合约：SCI4WebService-->**System.IO.FileNotFoundException:无法加载文件或程序集'System.Xml**，版本=2.0.5.0，区域性=neutral，PublicKeyToken=7cec85d7bea7798e'或其依赖项之一。哦，特别是阿尔基沃中心系统。
在System.ModuleHandle.ResolveType（Int32 typeToken、RuntimeTypeHandle*typeInstArgs、Int32 typeInstCount、RuntimeTypeHandle*methodInstArgs、Int32 methodInstCount）
位于System.ModuleHandle.ResolveTypeHandle（Int32 typeToken、RuntimeTypeHandle[]TypeInstanceContext、RuntimeTypeHandle[]MethodInstanceContext）
位于System.Reflection.Module.ResolveType（Int32 metadataToken，类型[]genericTypeArguments，类型[]genericMethodArguments）
在System.Reflection.CustomAttribute.FilterCustomAttributeCord（CustomAttributeRecord caRecord，MetadataImport作用域，Assembly&LastAptCookAssembly，Module decoratedModule，MetadataToken decoratedToken，RuntimeType attributeFilterType，Boolean mustBeInheritable，Object[]属性、IList derivedAttributes、RuntimeType和attributeType、RuntimeMethodHandle和ctor、Boolean和ctorHasParameters、Boolean和isVarArg）
位于System.Reflection.CustomAttribute.GetCustomAttributes（模块decoratedModule、Int32 decoratedMetadataToken、Int32 pcaCount、RuntimeType attributeFilterType、Boolean mustBeInheritable、IList derivedAttributes）
位于System.Reflection.CustomAttribute.GetCustomAttributes（RuntimeType类型、RuntimeType类型、布尔继承）
位于System.RuntimeType.GetCustomAttributes（类型attributeType，布尔继承）
在System.Runtime.Serialization.DataContract.TryGetDCAttribute（类型、DataContractAttribute和DataContractAttribute）
在System.Runtime.Serialization.DataContract.GetStableName（类型、布尔值和hasDataContract）
在System.Runtime.Serialization.DataContract.GetCollectionStableName（类型类型、类型itemType、CollectionDataContractAttribute和collectionContractAttribute）
在System.Runtime.Serialization.CollectionDataContract.CollectionDataContractCriticalHelper..ctor（类型类型、CollectionKind种类、类型itemType、MethodInfo getEnumeratorMethod、MethodInfo addMethod、ConstructorInfo构造函数）
在System.Runtime.Serialization.CollectionDataContract.IsCollectionOrTryCreate（类型类型、布尔tryCreate、DataContract和DataContract、类型和项目类型、布尔构造函数或Required）
at System.Runtime.Serialization.CollectionDataContract.TryCreate（类型、DataContract和DataContract）
at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract（Int32 id，RuntimeTypeHandle-typeHandle，Type-Type）
在System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation（Int32 id，RuntimeTypeHandle，TypeType）
在System.Runtime.Serialization.DataContract.GetDataContract（RuntimeTypeHandle-typeHandle，Type，SerializationMode模式）
at System.Runtime.Serialization.DataContractSet.GetDataContract（类型clrType）
at System.Runtime.Serialization.DataContractSet.GetMemberTypeDataContract（DataMember DataMember）
at System.Runtime.Serialization.DataContractSet.AddClassDataContract（ClassDataContract-ClassDataContract）
at System.Runtime.Serialization.DataContractSet.Add（XmlQualifiedName名称，DataContract DataContract）
在System.Runtime.Serialization.DataContractSet.AddCollectionDataContract（CollectionDataContract CollectionDataContract）
at System.Runtime.Serialization.DataContractSet.Add（XmlQualifiedName名称，DataContract DataContract）
at System.Runtime.Serialization.DataContractSet.AddClassDataContract（ClassDataContract-ClassDataContract）
at System.Runtime.Serialization.DataContractSet.Add（XmlQualifiedName名称，DataContract DataContract）
在System.Runtime.Serialization.DataContractSet.AddCollectionDataContract（CollectionDataContract CollectionDataContract）
at System.Runtime.Serialization.DataContractSet.Add（XmlQualifiedName名称，DataContract DataContract）
at System.Runtime.Serialization.DataContractSet.AddClassDataContract（ClassDataContract-ClassDataContract）
at System.Runtime.Serialization.DataContractSet.Add（XmlQualifiedName名称，DataContract DataContract）
at System.Runtime.Serialization.DataContractSet.Add（类型）
在System.Runtime.Serialization.XsdDataContractExporter.Export（类型）中
位于System.ServiceModel.Description.MessageContractExporter.ExportType（类型类型、字符串部分名称、字符串操作名称、XMLSchematType和XSDTType）
位于System.ServiceModel.Description.DataContractSerializerMessageContractExporter.ExportBody（Int32 messageIndex，对象状态）
位于System.ServiceModel.Description.MessageContractExporter.ExportMessage（Int32 messageIndex，对象状态）
位于System.ServiceModel.Description.MessageContractExporter.ExportMessageContract（）处
位于System.ServiceModel.Description.DataContractSerializePropertyBehavior.System.ServiceModel.Description.IWsdlExportExtension.ExportContract（WsdlExporter导出器，WsdlContractConversionContext contractContext）
位于System.ServiceModel.Description.WsdlExporter.CallExtension（WsdlContractConversionContext contractContext，IWsdlExportExtension扩展名）
---内部ExceptionDetail堆栈跟踪的结束---
位于System.ServiceModel.Description.ServiceMetadataBehavior.MetadataExtensionInitializer.GenerateMetadata（）处
位于System.ServiceModel.Description.ServiceMetadataExtension.EnsureInitialized（）处
位于System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.InitializationData.InitializeFrom（ServiceMetadataExtension扩展名）
位于System.ServiceModel.Description.ServiceMetadataExtension.HttpGetImpl.GetInitData（）处
在System.ServiceModel上