pbtxt file issue?

Hi - amazing work by the way. I've upgraded to 5.1.0 from an older version and see I now have to supply a config (.pbtxt ) as well as a .pb file to use the readNetFromTensorflow function. I've grabbed both files from https://github.com/opencv/opencv/wiki/TensorFlow-Object-Detection-API. I'm using MobileNet-SSD v1.

When running I get the following error:

ReadNetFromTensorflow - OpenCV Error: (nodesMapIt != nodesMap.end()) in sortByExecutionOrder, in file ../node_modules/opencv-build/opencv/opencv/modules/dnn/src/tensorflow/tf_graph_simplifier.cpp, line 860, status -215

Any help would be appreciated. Thanks.