tensorflow opencv python project bug

i have a tensorflow with opencv with trained model having error while running, it was wokring properly but when i changed the computer it shows error
File "/Users/mostafaehab/e-lpr/project-car/main.py", line 315, in <module>
possible_plates = findPlate.find_possible_plates(img)
File "/Users/mostafaehab/e-lpr/project-car/main.py", line 171, in find_possible_plates
plate, characters_on_plate, coordinates = self.check_plate(input_img, cnts)
File "/Users/mostafaehab/e-lpr/project-car/main.py", line 150, in check_plate
after_clean_plate_img, plateFound, coordinates = self.clean_plate(after_validation_img)
File "/Users/mostafaehab/e-lpr/project-car/main.py", line 126, in clean_plate
_, contours, _ = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)