IdentityModelStackTrace

[MissingMethodException: Method not found: 'System.Security.Cryptography.X509Certificates.X509Certificate2 System.Net.Http.HttpRequestMessageExtensions.GetClientCertificate(System.Net.Http.HttpRequestMessage)'.]
   Thinktecture.IdentityModel.Tokens.Http.HttpAuthentication.Authenticate(HttpRequestMessage request) in c:\etc\dropbox\source\thinktecture\Thinktecture.IdentityModel.40\IdentityModel\Thinktecture.IdentityModel\Tokens\Http\HttpAuthentication.cs:111
   Thinktecture.IdentityModel.Tokens.Http.AuthenticationHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) in c:\etc\dropbox\source\thinktecture\Thinktecture.IdentityModel.40\IdentityModel\Thinktecture.IdentityModel\Tokens\Http\AuthenticationHandler.cs:54
   System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +41
   System.Web.Http.HttpServer.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +347
   System.Net.Http.HttpMessageInvoker.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +55
   System.Web.Http.WebHost.HttpControllerHandler.BeginProcessRequest(HttpContextBase httpContextBase, AsyncCallback callback, Object state) +316
   System.Web.Http.WebHost.HttpControllerHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +77
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +268
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155