When codes are compiled in debug mode, no error. When compiled with release mode, got the following error

Could not load file or assembly 'System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
System.IO.FileNotFoundException: Could not load file or assembly 'System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
File name: 'System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializerContract.CanSerialize(Type type)
   at System.Xml.Serialization.TempAssembly.LoadGeneratedAssembly(Type type, String defaultNamespace, XmlSerializerImplementation& contract)
   at System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings, Type type)
   at System.ServiceModel.Description.XmlSerializerHelper.FromMappingsViaReflection(XmlMapping[] mappings, Type type)
   at System.ServiceModel.Description.XmlSerializerHelper.FromMappings(XmlMapping[] mappings, Type type)
   at System.ServiceModel.Description.XmlSerializerOperationBehavior.Reflector.SerializerGenerationContext.CreateSerializersFromMappings(XmlMapping[] mappings, Type type)

I use System.ServiceModel v4.10.3 and Service Reference to call and external SOAP service.

Sorry, I could not provide code snapshot…