This article, at http://twiki.org/cgi-bin/view/Support/ApacheUpgradeTaintError

is also interesting, same version of Perl, same error message, and the following answer

"It looks like =Net::SMTP and/or IO::Socket got more strict in regards to taint checking."

The script that crashed uses Net::SMTP, but it hadn't got into _that_ subroutine when it crashed.

Peter