My gratitude to the anonymous monk who reminded me of the power '$!' and a simple 'or die'. Permissions issue, and my application now seems to be writing session data to the file store.

$ymd->{'s'}->flush() or die "Died attempting to flush session paramete
+rs to the file store: ", $!;
[download]

Now to test the redirect and the preservation of session.

Thanks folks,
-- Hugh