The reason for the error is as Mad Hatter stated:

$message = s/<[>]*>//g;
[download]

The reason is that the above code is short for the following:

$message = $_ =~ s/<[>]*//g;
[download]

and you do not have anything in $_

That said, I would follow Limbic~Region's advice and check out CPAN modules for parsing out HTML.

update: There were my's in front of $message that were dropped. Also that as Limbic~Region already mentioned that you probably wanted the negated character class.

-enlil