outgoing url in mvc generated based on the current routing schema.
because your Information action method require id parameter, and your route collection has id of your current requested url(/Admin/Information/5), id parameter automatically gotten from existing route collection values.
to solve this problem you should use UrlParameter.Optional:
<a href="https://stackoverflow.com/questions/19107061/@Url.Action("Information", "Admin", new { id = UrlParameter.Optional })">Add an Admin</a>