UserData property of FormsAuthenticationTicket is empty despite being set

RedictFromLoginPage overwrites your cookie. Remove this line and redirect manually (Response.Redirect).

This is a similar answer I answered few days ago.

https://stackoverflow.com/a/16365000/296861

You cannot use FormsAuthentication.SetAuthCookie or FormsAuthentication.RedirectFromLoginPage if you create FormsAuthenticationTicket by yourself.