Allow downloading mdb file from ASP.Net page

I would like to let users download a file after they click a button. I just use Response.Redirect("~/123.mdb") to handle this situation. 

But, an error message is shown: 
"There is no build provider registered for the extension '.mdb'. You can register one in the section in machine.config or web.config"

To Deal with this issue, go to web.config, add a fileExtension element in web.config

FileExtensions in web.config