the command does not produce an error message

Unfortunately IIS doesn't capture errors and save them in an error log like Apache, so this is one reason why you would be unaware of the error. The browser will not necessarily give you any further information unless you ask it to. One way of doing this is with:

use CGI::Carp qw(fatalsToBrowser);

Which will throw errors to the browser. Regards your specific file error, is the permission modes set for ALL users? You may also need to set the directory permissions too. If IIS is running as a guest user, they may not have permission to access the file. This is the same with any webserver and is part of the security measures to ensure protected files cannot be tampered with.