Web Api won’t download file using jQuery Ajax and Basic Auth

I am using the ASP.NET Web API to build a prototype of a web service (and site) which has a method to download a file. When the user on the front-end presses the export button a jQuery ajax GET request is made and received by the controller which on it’s turn calls the method named Excel (shown below). The method runs without any problem and finishes. When I look in Chrome at the header (see https://skydrive.live.com/redir?resid=2D85E5C937AC2BF9!77093) it receives the response with (as far as I am concerned) all the right headers.

Customized authorization attribute in MVC 4 with Roles

I have created a customized role base authorization attribute.My idea is that when a user with role name “employee” Log In should not be allowed to access the “admin” page through URL. But when I implement the [MyRoleAuthorization] in Employee controller and Log In the error says “This webpage has a redirect loop”.
This is code for [MyRoleAuthorization]