Reading from ProtoFile - openpose COCO model example

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I am trying to run the openpose example https://github.com/opencv/opencv/blob... using the COCO model.

However when I compile and run (my executable is "kpd" for "Key Point Detection", I get the following error about the file being open

kpd -i /home/brian/Pictures/MyPic/IMG20180801205312.jpg -m pose_iter_440000.caffemodel -p pose_deploy_linevec.prototxt

OpenCV(3.4.1) Error: Unspecified error (FAILED: fs.is_open(). Can't open "true") in ReadProtoFromTextFile, file /home/brian/Progams/opencv/modules/dnn/src/caffe/caffe_io.cpp, line 1119 terminate called after throwing an instance of 'cv::Exception' what(): OpenCV(3.4.1) /home/brian/Progams/opencv/modules/dnn/src/caffe/caffe_io.cpp:1119: error: (-2) FAILED: fs.is_open(). Can't open "true" in function ReadProtoFromTextFile

Aborted (core dumped)

It doesn't appear to matter when the prototxt file is in the same folder or not, or whether I use absolute paths or not. I've also tried different models to no avail.

It's probably something simple, but I'm just getting started, so a bit green at OpenCV.

Thanks in Advance