The problem you are having is that you are trying to use Win32::Process::KillProcess() on a $pid returned by fork.

Under AS 5.6.1, fork is a simulation of the unix fork, and it is done using native threads, not processes. This can be confirmed by printing out the $pid returned by fork. On my system they always come back as a negative number but process ids are always positive. You can also see the second thread come into existance, and disappear if you watch the Task Manager.

To kill the forked 'process', just use the standard perl kill function.  kill 9, $pid;.

#! perl -slw
use strict;
use Config;
use Win32::Event;
use Win32::Process;
$|++;

#print $Config{sig_name};

my $event = Win32::Event->new(1, 0, 'test');
if (not defined(my $pid = fork())) {
    warn "can not fork: $!\n";
    return;
}
elsif ($pid) {
    print "Parent processid: $$; child:$pid";
    if($event->wait( 5000 )) {
        print 'The child signalled and terminated';
    }
    else {
        print 'Parent: child continuing after 5 secs';
        if($event->wait( 5000 )) {
            print 'The child signalled and terminated';
        }
        else {
            print 'Parent: child still continuing after 10 secs';
            my $exitCode = 0;
            print "Parent: Attempting to kill processid $pid";
#            Win32::Process::KillProcess( $pid, $exitCode ) or warn $^
+E;
#            print "Parent: KillProcess returned: $exitCode";
            kill 9, $pid or die $!;
            print "Parent: KillProcess returned: $?";
        }
    }
    print "Parent dying";
}
else {
    for (1..20) {
        print "Child process: $$";
        sleep 1;
    }
    print "Child: signalling parent";
    $event->set;
    print "Child dying";
    exit 12345;
}
__END__
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Output

C:\test>217881
Parent processid: 273; child:-295
Child process: -295
Child process: -295
Child process: -295
Child process: -295
Child process: -295
Parent: child continuing after 5 secs
Child process: -295
Child process: -295
Child process: -295
Child process: -295
Child process: -295
Parent: child still continuing after 10 secs
Parent: Attempting to kill processid -295
Parent: KillProcess returned: 0
Parent dying

C:\test>
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