Traceback error in Windows

[Eunsuh]

Traceback (most recent call last):
File "pingpong.py", line 59, in
observation.disable_fog = False
AttributeError: 'RequestObservation' object has no attribute 'disable_fog'

There is 'disable_fog' attribute in 'RequestObservation', but it cannot read the attribute and generates the error. The code works well if I just erase that line occuring the problem.