Yikes. To echo what others have said: "Upgrade your perl!" (HP-UX 11.00 (now out of date itself) shipped with perl 4.0). HP-UX 11.11 now ships with perl 5.8.x. HP themselves make a pre-packaged version of Perl available
Hope this helps.

Update: After your update: Are you sure that the more recent version of perl that you installed is the one being used. IIRC, HP's distribution installs to /opt/perl5/bin/perl. You should check yourself with something like swlist -l file perl | grep perl$, and then make sure that that copy of perl is in your PATH before the default OS installation.