Razor Exception

[InvalidOperationException: Could not determine the code language for "~/_appstart.cshtml".]
   System.Web.WebPages.Razor.WebPageRazorHost.GetCodeLanguage() +15771
   System.Web.WebPages.Razor.WebPageRazorHost..ctor(String virtualPath, String physicalPath) +100
   System.Web.WebPages.Razor.WebRazorHostFactory.CreateHost(String virtualPath, String physicalPath) +28
   System.Web.WebPages.Razor.WebRazorHostFactory.CreateHostFromConfigCore(RazorWebSectionGroup config, String virtualPath, String physicalPath) +276
   System.Web.WebPages.Razor.WebRazorHostFactory.CreateHostFromConfig(String virtualPath, String physicalPath) +57
   System.Web.WebPages.Razor.RazorBuildProvider.CreateHost() +17
   System.Web.WebPages.Razor.RazorBuildProvider.EnsureGeneratedCode() +65
   System.Web.WebPages.Razor.RazorBuildProvider.get_CodeCompilerType() +36
   System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider) +65
   System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders() +218
   System.Web.Compilation.BuildProvidersCompiler.PerformBuild() +40
   System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) +8967366
   System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +320
   System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +111
   System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound) +125
   System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp) +52
   System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(String virtualPath, Type requiredBaseType) +28
   System.Web.WebPages.VirtualPathFactoryManager.CreateInstance(String virtualPath) +270
   System.Web.WebPages.ApplicationStartPage.<ExecuteStartPage>b__6(String vpath) +26
   System.Web.WebPages.ApplicationStartPage.ExecuteStartPageInternal(HttpApplication application, Action`1 monitorFile, Func`2 fileExists, Func`2 createInstance, IEnumerable`1 supportedExtensions) +152
   System.Web.WebPages.ApplicationStartPage.ExecuteStartPage(HttpApplication application, Action`1 monitorFile, Func`2 fileExists, Func`2 createInstance, IEnumerable`1 supportedExtensions) +41

[HttpException (0x80004005): Exception of type 'System.Web.HttpException' was thrown.]
   System.Web.WebPages.ApplicationStartPage.ExecuteStartPage(HttpApplication application, Action`1 monitorFile, Func`2 fileExists, Func`2 createInstance, IEnumerable`1 supportedExtensions) +88
   System.Web.WebPages.ApplicationStartPage.ExecuteStartPage(HttpApplication application) +287
   System.Web.WebPages.WebPageHttpModule.StartApplication(HttpApplication application, Action`1 executeStartPage, EventHandler applicationStart) +113
   System.Web.WebPages.WebPageHttpModule.StartApplication(HttpApplication application) +71
   System.Web.WebPages.WebPageHttpModule.Init(HttpApplication application) +156
   System.Web.HttpApplication.InitModulesCommon() +80
   System.Web.HttpApplication.InitModules() +43
   System.Web.HttpApplication.InitInternal(HttpContext context, HttpApplicationState state, MethodInfo[] handlers) +828
   System.Web.HttpApplicationFactory.GetNormalApplicationInstance(HttpContext context) +304
   System.Web.HttpApplicationFactory.GetApplicationInstance(HttpContext context) +107
   System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr) +327