You will face this weird issue when you upgrade SimpleSecurity from MVC 4 to MVC 5 and this is an issue that you’ll see:

Attempt by security transparent method 'WebMatrix.WebData.PreApplicationStartCode.Start()' to access security critical method 'System.Web.WebPages.Razor.WebPageRazorHost.AddGlobalImport(System.String)' failed.

I did some research and found that others were having the same issue. Well it turns out I did not follow the instructions exactly.  Here is one note in the instructions I did not pay close attention to.

Note: Microsoft-Web-Helpers has been replaced  with Microsoft.AspNet.WebHelpers. You should remove the old package first,  and then install the newer package.

I opened up the NuGet Package Manager and installed the package Microsoft.AspNet.WebHelpers and things started to work.  Note that when you create a new MVC 5 application and try to incorporate SimpleSecurity or SimpleMembership you will hit the same issue because Microsoft.AspNet.WebHelpers  is not installed by default.  It has to be present for SimpleMembership to run correctly.

I verified that all of the features in the reference application are working correctly after the upgrade.  Even the generation of the emails using Postal worked, which I was not sure of because of the upgrade of Razor as well.

One change I needed to make to the SimpleSecurity assembly was to remove the filters AuthorizeAttribute and BasicAuthorizeAttribute and put them in a separate assembly.  I did this because they are dependent upon MVC and Web API assemblies.  So now there is a version for MVC 4 and another for MVC 5. Please check https://simplesecurity.codeplex.com/SourceControl/latest for SimpleSecurity Project Source Code. Hope it helps