Never the less, you can tell CGI::Carp to send it's error messages to a file you specify if you want, and that might help with this point:

IIS doesn't send CGI::Carp messages to the log file, but directly to the browser.

You can do this by:

use CGI::Carp qw/carpout/;
use FileHandle;

my $fh = new FileHandle;  
$fh->open("logfile.log") or die "Failed to open logfile: $!";

carpout($fh);
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Of course, if you don't like FileHandle, you can open a standard filehandle and pass that to carpout too. Read the docs.