NetCDF 3 does not support type |S4

Please, can someone explain how to resolve the error below:

File "/opt/cdstoolbox/cdscompute/cdscompute/cdshandlers/services/handler.py", line 59, in handle_request
    result = cached(context.method, proc, context, context.args, context.kwargs)
  File "/opt/cdstoolbox/cdscompute/cdscompute/caching.py", line 108, in cached
    result = proc(context, *context.args, **context.kwargs)
  File "/opt/cdstoolbox/cdscompute/cdscompute/services.py", line 124, in __call__
    return p(*args, **kwargs)
  File "/opt/cdstoolbox/cdscompute/cdscompute/services.py", line 60, in __call__
    return self.proc(context, *args, **kwargs)
  File "/home/cds/cdsservices/services/python_service.py", line 38, in execute
    raise exceptions.InternalError(logging + traceback, '')
cdsclient.exceptions.InternalError: Traceback (most recent call last):
  File "/opt/cdstoolbox/cdscdm/cdscdm/io.py", line 358, in dataset_to_netcdf
    dataset.to_netcdf(output_path, **kwargs_compress)
  File "/usr/local/lib/python3.6/site-packages/xarray/core/dataset.py", line 1567, in to_netcdf
    invalid_netcdf=invalid_netcdf,
  File "/usr/local/lib/python3.6/site-packages/xarray/backends/api.py", line 1082, in to_netcdf
    dataset, store, writer, encoding=encoding, unlimited_dims=unlimited_dims
  File "/usr/local/lib/python3.6/site-packages/xarray/backends/api.py", line 1128, in dump_to_store
    store.store(variables, attrs, check_encoding, writer, unlimited_dims=unlimited_dims)
  File "/usr/local/lib/python3.6/site-packages/xarray/backends/common.py", line 255, in store
    variables, check_encoding_set, writer, unlimited_dims=unlimited_dims
  File "/usr/local/lib/python3.6/site-packages/xarray/backends/common.py", line 293, in set_variables
    name, v, check, unlimited_dims=unlimited_dims
  File "/usr/local/lib/python3.6/site-packages/xarray/backends/scipy_.py", line 210, in prepare_variable
    self.ds.createVariable(name, data.dtype, variable.dims)
  File "/usr/local/lib64/python3.6/site-packages/scipy/io/netcdf.py", line 391, in createVariable
    raise ValueError("NetCDF 3 does not support type %s" % type)
ValueError: NetCDF 3 does not support type |S4


Thank you!