Compiler Error: System.InvalidOperationException: Sequence contains no elements

i have the same problem! How to fix it? Help me!!!
Error building Player: Exception: Failed to run assembly converter with command line -platform=wp80 "Temp/StagingArea\Assembly-CSharp-firstpass.dll" "Temp/StagingArea\Assembly-CSharp.dll" "Temp/StagingArea\UnityEngine.dll" "Temp/StagingArea\UnityEngine.UI.dll" "Temp/StagingArea\WinRTLegacy.dll".
System.Exception: Failed to resolve type System.Net.Sockets.TcpClient. Is type unavailable in target framework?
� Unity.MetadataContainer.ResolveType(TypeReference type)
� Unity.MetadataContainer.GetAssemblyForType(TypeReference type)
� Unity.AssemblyWrapper.CreateMethodWrapper(MetadataContainer metadata, TypeWrapper typeWrapper, MethodDefinition method)
� Unity.AssemblyWrapper.GetCallableMethods(TypeWrapper typeWrapper, TypeDefinition type, Boolean publicOnly)
� Unity.AssemblyWrapper.AddType(TypeReference type)
� Unity.GetTypesStep.Visit(TypeDefinition type)
� Unity.TypeDefinitionDispatcher.DispatchType(TypeDefinition type)
� Unity.TypeDefinitionDispatcher..ctor(ModuleDefinition module, ITypeDefinitionVisitor visitor)
� Unity.GetTypesStep.ProcessModule()
� Unity.ModuleStep.Execute()
� Unity.Step.Execute(OperationContext operationContext, IStepContext previousStepContext)
� Unity.Operation.Execute()
� Unity.Program.Main(String[] args)