NetCDF output for Gregorian calendar

I am trying to run a AMIP configuration of UKESM1.1 (u-db167) using the Gregorian calendar and producing netcdf data. The limited set of diagnostics I am using all use time profile TMONMN, usage profile UPM_NC and write to nc0. I think I have set these to do things every “Real Month”. When I tried to run I got a failure:
???!!!???!!!???!!!???!!!???!!! ERROR ???!!!???!!!???!!!???!!!???!!!
? Error code: 102
? Error from routine: NCFILE_WRITE_TIME_DIM
? Error message: Unknown unit code for output times, unitin = 7
? Error from processor: 0
? Error number: 31

How do I fix this?