It appears that if you have used CPAN to augment your default Perl installation, then Security Update 2009-001 "kills" Perl, so your scripts won't run. There is a more discussion about this in this Apple Discussions thread.
The fix mentioned in that thread that worked for me was the following, all done in Terminal:
$ mkdir -p /SourceCache
$ cd /SourceCache
$ curl -O http://cpan.mirror.solnet.ch/authors/id/G/GB/GBARR/IO-1.2301.tar.gz
$ tar xzf IO-1.2301.tar.gz
$ cd IO-1.2301
$ perl Makefile.PL
$ make
$ make install
Note that for some of the above commands, you must be logged in as root, or run using sudo.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090219082024982