While perl modules are case sensitive , some filesystems are not; there already exists a Config module, so "config" or "CoNFiG" or any variation is a bad name to choose, its already taken

Also, all lowercase names are reserved for pragmas

Also, you shouldn't be "including" lib.cgi or login.cgi or any such thing, you're already making modules, so make them all modules, something like this

MyApp::Config
MyApp::Login
MyApp::Lib
MyApp::Screen::Login
MyApp::Screen::Lib
[download]

Something along those lines,

You can find more discussions on naming modules in Re: RFC: Automatic logger module