You can track down the location of the eval by setting up a die handler that prints a stack trace. For example:

$SIG{__DIE__} = sub {
    my @stack;
    my $i = 0;
    while(my($package, $file, $line) = caller($i++)) {
      push @stack, "  package $package, file $file, line $line\n";
    }
    die @_, @stack;
};
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Note that I have not tested this with FastCGI.

First, though, you should do a quick grep of the source for the word 'simple'. That's easier and should work fine in this case.