Inheritance sec rules violated by type: 'System.Net.Http.WebRequestHandler'
<p>I am Trying to access Active Directory data through graph API. i am getting the following error on running the application. </p>

<p><strong>Description:</strong> An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.</p>

<p><strong>Exception Details:</strong>  "System.TypeLoadException: <strong>Inheritance security rules violated by type: 'System.Net.Http.WebRequestHandler'. Derived types must either match the security accessibility of the base type or be less accessible</strong>."</p>

<p><strong>Source Error:</strong></p>

<p>An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.</p>

<p><strong>Stack Trace:</strong></p>

<pre><code>[TypeLoadException: Inheritance security rules violated by type: 'System.Net.Http.WebRequestHandler'. Derived types must either match the security accessibility of the base type or be less accessible.]
   Microsoft.Owin.Security.OpenIdConnect.OpenIdConnectAuthenticationMiddleware.ResolveHttpMessageHandler(OpenIdConnectAuthenticationOptions options) +0
   Microsoft.Owin.Security.OpenIdConnect.OpenIdConnectAuthenticationMiddleware..ctor(OwinMiddleware next, IAppBuilder app, OpenIdConnectAuthenticationOptions options) +996
   lambda_method(Closure , OwinMiddleware , IAppBuilder , OpenIdConnectAuthenticationOptions ) +54

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) +0
   System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments) +92
   System.Delegate.DynamicInvokeImpl(Object[] args) +117
   System.Delegate.DynamicInvoke(Object[] args) +12
   Microsoft.Owin.Builder.AppBuilder.BuildInternal(Type signature) +236
   Microsoft.Owin.Builder.AppBuilder.Build(Type returnType) +21
   Microsoft.Owin.Host.SystemWeb.OwinAppContext.Initialize(Action`1 startup) +565
   Microsoft.Owin.Host.SystemWeb.OwinBuilder.Build(Action`1 startup) +58
   Microsoft.Owin.Host.SystemWeb.OwinHttpModule.InitializeBlueprint() +95
   System.Threading.LazyInitializer.EnsureInitializedCore(T&amp; target, Boolean&amp; initialized, Object&amp; syncLock, Func`1 valueFactory) +115
   System.Threading.LazyInitializer.EnsureInitialized(T&amp; target, Boolean&amp; initialized, Object&amp; syncLock, Func`1 valueFactory) +72
   Microsoft.Owin.Host.SystemWeb.OwinHttpModule.Init(HttpApplication context) +96
   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +523
   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +176
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +364
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +303

[HttpException (0x80004005): Exception has been thrown by the target of an invocation.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +770
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +95
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +195


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.6.1069.1 
</code></pre>

<p>As i am a beginner i am struck with the error. Could any one please let me know what needs to be done to overcome this error</p>