If the received power is less than -27.5 dBm on the MutliFiber Pro meter when saving a reference, the meter will not allow you to save the reference you just carried out. It will flash the "Err" on the instrument before swapping to the LOSS menu/measurement screen.
This could be either a dirt issue or a damaged cord/port. If you do not have an MPO/MTP cleaner, you will need to get one. It is also highly recommended to have an MPO/MTP inspection device too.