There may be other reasons, but if "hard" 13C 90 pulse is longer than probe specification - you can check this value yourself, Biopack calibration may set decoupler power to a value above the limit set in the pulse sequences. Then routine will fail with an error something like "dpwr too high, don't fry the probe".
Other reasons might be trivial - your sample being too dilute, cables not connected properly or "other hardware issue" - which can of course include lot's of things. If you can confirm this failure with a reliably good 15N, 13C-labeled sample and you are confident in cabling of the instrument - you should probably ask your facility engineer to check the spectrometer and the probe.
