I have a simple question and I hope I can get help

I am using phoca download 2.1.6 version. It is really a great componet, lots of thanks to developers.
My question is; I have a user group with the name of "registered-teachers". Some files can be downloaded only by this group. When a normal "registered user" try to download one of these files, it says "you must login". What I want is; when a normal registered user try to download one of these files, it should say " you don't have permission to download this file, only teachers can download it". I wonder whether such a thing is possible or not?