Link to a protected ED category leads to 404

I have a category on my forum which is restricted to specific user groups. When I provide the direct link to a user it leads to a 404 error if clicked when he is not logged in. If he is logged in the link works fine and points to the restricted area.
Is it possible to serve a login page if the user is not logged in? I think it is a bit more friendly and causes less confusion. Now people think that the link is wrong .....
Maybe make it generic. When people try to access a category for which they are not enabled show a login page with some message saying that they have no access to that area?