求高手帮忙，我安装mvc4报错如下图，谢谢
说明: 执行当前 Web 请求期间，出现未经处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。
异常详细信息: System.IO.FileLoadException: 未能加载文件或程序集“System.Net.Http”或它的某一个依赖项。拒绝访问。
源错误:
执行当前 Web 请求期间生成了未经处理的异常。可以使用下面的异常堆栈跟踪信息确定有关异常原因和发生位置的信息。
程序集加载跟踪: 下列信息有助于确定程序集“System.Net.Http”未能加载的原因。
警告: 程序集绑定日志记录被关闭。
要启用程序集绑定失败日志记录，请将注册表值 HKLM\Software\Microsoft\Fusion!EnableLog设置为 1。
注意: 会有一些与程序集绑定失败日志记录关联的性能损失。
要关闭此功能，请移除注册表值 [HKLM\Software\Microsoft\Fusion!EnableLog]。
堆栈跟踪:
[FileLoadException: 未能加载文件或程序集“System.Net.Http”或它的某一个依赖项。拒绝访问。]
[FileLoadException: 未能加载文件或程序集“System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a”或它的某一个依赖项。拒绝访问。]
System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0
System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +34
System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +347
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +83
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +17
System.Reflection.Assembly.Load(String assemblyString) +29
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +38
[ConfigurationErrorsException: 未能加载文件或程序集“System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a”或它的某一个依赖项。拒绝访问。]
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +728
System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +196
System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +45
System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +172
System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +91
System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +111
System.Web.Compilation.BuildManager.ExecutePreAppStart() +154
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +616
[HttpException (0x80004005): 未能加载文件或程序集“System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a”或它的某一个依赖项。拒绝访问。]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +662
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +96
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +189
