This is a known issue Russell and has been going on for years. Reckon blame Microsoft. There are several KB articles on it but to be frank I changed to gmail and got over the issue rather than try to convince Reckon that Microsoft weren't going to change so Reckon needed to get on top of it. Sadly, that went ignored too.
Thanks, how awesome to fork out subscription costs to have up to date software that will not work anyway. If I could get the invoices to send I would love to send an invoice to reckon for wasting my time!!!