Forms authentication on HTML Files

I have a sub-domain that has html files and I want to secure them so that they are only accessible once the user has successfully  logged in .

First Method  i have tried adding the below :

 under forms authentication <compilation><buildProviders><add extension=".html" type="System.Web.Compilation.PageBuildProvider" /><add extension=".htm" type="System.Web.Compilation.PageBuildProvider" /></buildProviders></compilation>
AND<system.webServer><handlers><add name="HTML" path="*.html" verb="GET, HEAD, POST, DEBUG"   type="System.Web.UI.PageHandlerFactory" resourceType="Unspecified" requireAccess="Script" /><add name="HTM" path="*.htm" verb="GET, HEAD, POST, DEBUG" type="System.Web.UI.PageHandlerFactory" resourceType="Unspecified" requireAccess="Script" /></handlers></system.webServer>

second method :

<modules runAllManagedModulesForAllRequests="true" /></modules>

Both Methods , when I try to log into the sub-domain only   --    http://ss.aio.com

or

 http://ss.aio.com/x/index.html ,

im getting : 500 - internal server Error !!!!!!!

THE HTML FILES ARE IN DIRECTORIES AND I HAVE ALSO DISABLED DIRECTORY BROWSING IN IIS 

any hint please ??