CDO

I would like to calculate multi year seasonal mean by:

cdo yseasmean MPI-ESM-LR-CLM4.8.17_wet_power.nc MPI-ESM-LR-CLM4.8.17_wet_power_sm.nc

but I got the following error messages:

cdf_put_vara_double : ncid = 131072 varid = 3 val0 = -999.000000
cdf_put_vara_double : varname = pr
Error (cdf_put_vara_double) : NetCDF: Numeric conversion not representable

I do not understand why I got this error because _FillValue is float:

netcdf MPI-ESM-LR-CLM4.8.17_wet_power {
dimensions:
longitude = 464 ;
latitude = 201 ;
time = 5479 ;
variables:
float longitude(longitude) ;
longitude:long_name = "longitude" ;
longitude:standard_name = "lon" ;
longitude:units = "degrees_east" ;
float latitude(latitude) ;
latitude:long_name = "latitude" ;
latitude:standard_name = "lat" ;
latitude:units = "degrees_north" ;
double time(time) ;
time:long_name = "time" ;
time:standard_name = "time" ;
time:units = "days since 1949-12-1 00:00:00" ;
float pr(time, latitude, longitude) ;
pr:_FillValue = -999.f ;
pr:long_name = "precipitation" ;
pr:standard_name = "precipitation_flux" ;
pr:units = "mm" ;
pr:cell_methods = "time: mean" ;

// global attributes:
:history = "Mon Jun 19 09:52:46 2017: ncatted -O -a _FillValue,pr,m,f,-999 MPI-ESM-LR-CLM4.8.17_wet_power.nc\n",
"Mon Jun 19 09:22:52 2017: ncatted -O -a missing_value,,d,, MPI-ESM-LR-CLM4.8.17_wet_power.nc" ;
}

I tried to modify the _FillValue from -999.000000 to -999 by

cdo setmissval,-999 MPI-ESM-LR-CLM4.8.17_wet_power.nc MPI-ESM-LR-CLM4.8.17_wet_power2.nc

but I got the same error message.

Could someone write me how I should convert the _FillValue to -999?

Thank you for your response in advance!
Kind regards,
Beata