Error while trying to import

Traceback (most recent call last):
  File "/trytond/", line 79, in dispatch_request
    return endpoint(request, **request.view_args)
  File "/trytond/protocols/", line 44, in rpc
    return methods.get(request.rpc_method, _dispatch)(
  File "/trytond/", line 50, in auth_required
    return wrapped(*args, **kwargs)
  File "/trytond/protocols/", line 122, in wrapper
    return func(request, pool, *args, **kwargs)
  File "/trytond/protocols/", line 175, in _dispatch
    result = rpc.result(meth(*c_args, **c_kwargs))
  File "/trytond/model/", line 827, in import_data
    assert all(len(x) == len_fields_names for x in data)

It looks like the CSV file does not have for all lines the same number of columns.