From man perldiag:

       Can't reswap uid and euid
           (P) The setreuid() call failed for some reason in the
           setuid emulator of suidperl.

You might want to check the setreuid manual page. You should also note that there are differences between a BSD and a system V system when it comes to dealing with UID, EUID and SUID.

There is an interesting read about that on http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf.

Abigail