Unable to use 4-20mA DAC with RTC

Hi, I'm trying to use the DFRobot 4-20mA DAC on Arduino along with an RTC that is sharing the I2C bus (with a different address) using the DFRobot I2C expansion board. What happens is every time I try to run the RTC library code “rtc.refresh()”, the DAC stops working. I tried using a different RTC library, “RTCLib.h” but upon using that the DAC status is showing error. I'm stuck with this since a couple of days. Please help.