My favorite trick for debugging CGI scripts when you only have FTP access is to write a short shell-script wrapper like this:

#!/bin/sh -x

printf "Content-type: text/plain\n\n";
exec 2>&1

./downloads.pl
echo "Exited with status $?"

That will show you whatever errors you would see if you were running your script from the command-line on the server.

Of course, if you can look in your server's error log, that's simpler and quicker.