I wonder if $SIG{__DIE__} is exactly the problem here: the line in Math::BigInt::objectify() is:

Now, there is a precedence error here (I've reported that), but if can() returns false it shouldn't affect us, it should simply call $a[0]->new($k).

The code from Math::Pari::can() is:

$f = eval { loadPari($meth) };
return $f if defined $f;
return;
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.. which should correctly return undef if the loadPari() fails. However if some $SIG{__DIE__} is catching the loadPari() failure, maybe we're never getting to return from the eval. Or maybe the die handler is (inappropriately) reporting the error and the code is then successfully continuing.

I'd be tempted for starters to put a diagnostic in objectify() just after that line, to see if a) it reaches there, and b) $k has the correct value. I'd also hunt for a $SIG{__DIE__} handler, to check what exactly it is doing - generally, such handlers should almost always act only after checking they are not inside an eval. There may be a better way, but when I needed this some time ago for a logging module the code looked like this:

$SIG{__DIE__} = sub {
  # propagate the die if we're under an eval
  (defined($^S) && !$^S) or die(@_);
  # now do the real stuff
  ...
};
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.. but there may be a better way.

Hugo