how can I solve the error?

[KimYonghyun94]

OpenCV version: 3.3.1
Linux is fine! Python multiprocessing works.
OpenCV Error: Unspecified error (FAILED: fs.is_open(). Can't open "assets/deploy.prototxt") in ReadProtoFromTextFile, file /io/opencv/modules/dnn/src/caffe/caffe_io.cpp, line 1113
Traceback (most recent call last):
File "/content/head-pose-estimation/estimate_head_pose.py", line 161, in
main()
File "/content/head-pose-estimation/estimate_head_pose.py", line 57, in main
mark_detector = MarkDetector()
File "/content/head-pose-estimation/mark_detector.py", line 68, in init
self.face_detector = FaceDetector()
File "/content/head-pose-estimation/mark_detector.py", line 14, in init
self.face_net = cv2.dnn.readNetFromCaffe(dnn_proto_text, dnn_model)
cv2.error: /io/opencv/modules/dnn/src/caffe/caffe_io.cpp:1113: error: (-2) FAILED: fs.is_open(). Can't open "assets/deploy.prototxt" in function ReadProtoFromTextFile