assertion error (?) when loading yolo9000 with cv2.dnn.readNetFromDarknet

[average-everyman]

Hello, this is what I get:

model = cv2.dnn.readNetFromDarknet(path_to_model_config, path_to_model_weights)
cv2.error: OpenCV(4.5.1) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-i1s8y2i1\opencv\modules\dnn\src\darknet\darknet_io.cpp:632: error: (-215:Assertion failed) separator_index < line.size() in function 'cv::dnn::darknet::ReadDarknetFromCfgStream'

weights file was created as per instructions here:
https://github.com/philipperemy/yolo-9000#windows

cfg file was from here:
https://github.com/pjreddie/darknet/blob/1e729804f61c8627eb257fba8b83f74e04945db7/cfg/yolo9000.cfg

any ideas? I am a bit puzzled by this...