Thanks for the suggestion BrowserUk, I have reviewed the module code for Win32::MMF::Shareable, and after extensive debugging, I (think that I) have discoverred that the module might not be thread safe. I am doing some experiments at the moment to see if I could have independend sets of data both child and parents so they don't interfere with each other, as currently the child and parent share the same set of global data.

I tried your suggestion: I removed the use Win32::MMF::Shareable line at the start, which gets loaded at compile time, and then added require in each parent and child processes after the fork. The problem some how has gone away. The following is the test code I used:

#!C:/Perl/bin/perl -w
use strict;
use Data::Dumper;

if( fork )
{
  require Win32::MMF::Shareable;
  my $ns = tie( my %share, 'Win32::MMF::Shareable', 'share' ) || die;
  sleep(1);
  $share{parent} = 1;
  print Dumper(\%share);
}
else
{
  require Win32::MMF::Shareable;
  my $ns = tie( my %share, 'Win32::MMF::Shareable', 'share' ) || die;
  $share{child} = 1;
}
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Is this because the require is executed at run-time, which causes two different copy of Storable to be loaded at run-time, which in turn gets freed properly in their own instances?

And thanks again!