I have already been in touch with support via chat and the representative I spoke with seemed to know nothing about why the error was occurring.  The two users I was trying to add were new employees with absolutely no transactions in their record at all (as I attempted to add them as time tracking users immediately after adding them to the employee file) - so if the investigation is only looking into employees that have previous transactions, it needs to be expanded to all employees your customers are attempting to add as time tracking users.  Thank you for following up and I do hope to see this issue resolved permanently in the near future.