QuickBooks dilema

I have quick books 99 on my main computer. I wanted to let another person do some invoicing, so I put it ohn their computer. we both are running windows 98 se… When I try to back up the data from this computer to that one, it tells me, ” data from a newer version of quick books, cannot use”. I used the same installation cd on both computers.?#@! Wazupwidat and what do I do?