Yes with that warning message appearing your back office software will not be able to collect your sales information. Basically, that message means there is a Staff number that has started a transaction but not completed it. The best thing to do is, log on as each of your Staff members in turn and press CASH
on each one of them. When you press CASH
on at least one of them you should find that the drawer opens meaning that particular Staff was in the middle of a transaction. Once all staff have been cleared, try the report again and it should hopefully work.
Please do let me know if you get sorted.