first check if the hardware connections are as per the software port and pin assignment. if it is not possible the post the circuit diagram and the code you are using...........
Seems to be your crystal oscillator is deviating too much. Under what environment do you use the device, withiin room or in field? what if the capacitor value used for your RTC crystal 32.768KHz.
can you measure the oscillator frequency on a scope and see how much if the frequency.