The lines are:
&prescribed_aero_nl
prescribed_aero_datapath = '/glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/aero'
prescribed_aero_file = 'aero_1.9x2.5_L26_1850-2005_c091112.nc'
prescribed_aero_specifier = 'sulf:SO4', 'bcar1:CB1', 'bcar2:CB2', 'ocar1:OC1', 'ocar2:OC2', 'sslt1:SSLT01', 'sslt2:SSLT02',
'sslt3:SSLT03', 'sslt4:SSLT04', 'dust1:DST01', 'dust2:DST02', 'dust3:DST03', 'dust4:DST04'
prescribed_aero_type = 'INTERP_MISSING_MONTHS'but I don't think the problem is over there.The error your are getting implies that clim_modal_aero is set to true.
The variable clim_modal_aero is true only when modal aerosols are used in the climate calculation.
This is not the case in CAM4.
There is something wrong is in your setting and I am trying to figure out what.
Maybe you orginally built this case with another compset thet uses modal aersol (for instance F_AMIP_CAM5).
ANd if you didn't do a clean build, there might be something worng with your setting.
Please could you try to recreate the case from scratch (just do the sequence of CESM command using another casename).