SunTech Oscar 2 RTC Battery Replacement

I replaced the Real Time Clock battery on a SunTech Oscar 2 M250 Monitor and when I turned the device on the "rtc" warning appears. The monitor appears locked and the blood pressure readings programming does not run. When I remove the main batteries, the programmed time is lost and the "rtc" warning appears again. Does anyone know the procedure to resolve this issue? Thanks.