ERROR: Could not load file or assembly 'System.Diagnostics.Debug' or one of its dependencies

This is a C# Razor WebPages project... I can't seem to figure out what went wrong here. I've been trying to remove dependencies from my web.config file but nothing seems to work.

Can anyone help?

 [BadImageFormatException: Cannot load a reference assembly for execution.]

[BadImageFormatException: Could not load file or assembly 'System.Diagnostics.Debug' or one of its dependencies. Reference assemblies should not be loaded for execution. They can only be loaded in the Reflection-only loader context. (Exception from HRESULT: 0x80131058)] 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.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +225
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +110
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +22 System.Reflection.Assembly.Load(String assemblyString) +34
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +48

[ConfigurationErrorsException: Could not load file or assembly 'System.Diagnostics.Debug' or one of its dependencies. Reference assemblies should not be loaded for execution. They can only be loaded in the Reflection-only loader context. (Exception from HRESULT: 0x80131058)]
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +767
System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +256 System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +58
System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +281
System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +69 System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +137
System.Web.Compilation.BuildManager.ExecutePreAppStart() +172
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +848

[HttpException (0x80004005): Could not load file or assembly 'System.Diagnostics.Debug' or one of its dependencies. Reference assemblies should not be loaded for execution. They can only be loaded in the Reflection-only loader context. (Exception from HRESULT: 0x80131058)] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +532
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +111 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +714