Arduino Leo. Issues with thermocouple and rtc

Hi,

I'm working with the Arduino Leonardo. I want to measure temperatures using a k-type thermocouple (I'm using the Adafruit MAX31855 amplifier). This on it's own works fine.
I then want to log the measurements to an SD card. I have purchased a datalogging shield and an SD card. This also, on it's own, works fine.
I now want to add the date and time to the file I'm writing to on the SD card. The rtc, which is on board the datalogging shield provides both date and time. I have no problems logging date and time, nor any problems logging the temperature measurements. However, as soon as I want to combine all of the above, the temperature measurements become 0.00 all of a sudden.

Has anyone experienced any related issues and, more important, does anyone have suggestions as to how I can resolve this issue?

Thanks in advance
Kim