[Python] Getting [Errno 22] Invalid argument when trying to access data variables

I have a grib file containing reanalysis (an), ensemble mean (em), and ensemble spread (es) data. The dataset I access is the analysis data,

import xarray as xr
import cfgrib
file = 'C:/Users/Downloads/04292020_rean_ensmean_ensspread.grib'
ds = xr.open_dataset(file,engine = "cfgrib",filter_by_keys={'dataType': 'an'}) # an accesses analysis data

time = 5;
res = 2; #2 = half degree
[phi,theta] = np.meshgrid(ds.variables['longitude'][::res].values,ds.variables['latitude'][::res].values)
divergence = ds.variables['d'][time,:,::res,::res].values


I'm able to access longitude and latitude values just fine, but if I try to access one of the field variable's values like divergence, it returns this error every time. Here's the head data assuming it's useful:

# <bound method Dataset.head of <xarray.Dataset> Size: 20GB
# Dimensions: (time: 16, isobaricInhPa: 23, latitude: 721, longitude: 1440)
# Coordinates:
# number int32 4B ...
# * time (time) datetime64[ns] 128B 2020-04-29 ... 2020-04-29T23:00:00
# step timedelta64[ns] 8B ...
# * isobaricInhPa (isobaricInhPa) float64 184B 1e+03 975.0 ... 225.0 200.0
# * latitude (latitude) float64 6kB 90.0 89.75 89.5 ... -89.5 -89.75 -90.0
# * longitude (longitude) float64 12kB 0.0 0.25 0.5 ... 359.2 359.5 359.8
# valid_time (time) datetime64[ns] 128B ...
# Data variables: (12/13)
# d (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# cc (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# z (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# pv (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# r (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# clwc (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# ...
# crwc (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# t (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# u (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# v (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# w (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# vo (time, isobaricInhPa, latitude, longitude) float32 2GB ...
# Attributes:
# GRIB_edition: 1
# GRIB_centre: ecmf
# GRIB_centreDescription: European Centre for Medium-Range Weather Forecasts
# GRIB_subCentre: 0
# Conventions: CF-1.7
# institution: European Centre for Medium-Range Weather Forecasts
# history: 2025-03-23T18:13 GRIB to CDM+CF via cfgrib-0.9.1...>

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