Error in Assertion failed (!empty()) in detectMultiScale

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Hi,

I am using ROS + Open Cv and recently coded a code but receive this error:Error in Assertion failed (!empty()) in detectMultiScale I check my directory, the .xml file is indicated as it suppose to. Kindly do help me.

P.S. I did another test code with using Open Cv inputs (without ROS), it work perfectly.

Code:

#!/usr/bin/env python
from __future__ import print_function

import numpy as np
import roslib
import sys
import rospy
import cv2 
from std_msgs.msg import String
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

class image_converter:

  def __init__(self):
    self.image_pub = rospy.Publisher("image_topic_2",Image)

    self.bridge = CvBridge()
    self.image_sub = rospy.Subscriber("/camera/rgb/image_raw",Image,self.callback)

  def callback(self,data):
    try:
      cv_image = self.bridge.imgmsg_to_cv2(data, "bgr8")
      cv_image2 =  self.bridge.imgmsg_to_cv2(data, "bgr8")
    except CvBridgeError as e:
      print(e)

    (rows,cols,channels) = cv_image.shape
    if cols > 60 and rows > 60 :
      cv2.circle(cv_image, (50,50), 10, 255)
    cv2.imshow('cv_image',cv_image)
    cv2.waitKey(3)
    face_cascade = cv2.CascadeClassifier('compare/data/haarcascade_frontalface_alt.xml')
    test = face_cascade.load('compare/data/haarcascade_frontalface_alt.xml')
    print(test)
    gray = cv2.cvtColor(cv_image2, cv2.COLOR_BGR2GRAY)
    faces = face_cascade.detectMultiScale(gray, scaleFactor=1.5, minNeighbors=5)
    cv2.imshow('gray',gray)
    for (x, y, w, h) in faces:
        #print(x,y,w,h)
        roi_gray = gray[y:y+h, x:x+w] #(ycord_start, ycord_end)
        roi_color = cv_image2[y:y+h, x:x+w]
        img_item = "my-image.png"
        cv2.imwrite(img_item, roi_color)

        color = (255, 0, 0) #BGR 0-255 
        stroke = 2
        end_cord_x = x + w
        end_cord_y = y + h
        cv2.rectangle(cv_image2, (x, y), (end_cord_x, end_cord_y), color, stroke)
        #subitems = smile_cascade.detectMultiScale(roi_gray)
        #for (ex,ey,ew,eh) in subitems:
        #   cv2.rectangle(roi_color,(ex,ey),(ex+ew,ey+eh),(0,255,0),2)
    # Display the resulting frame

    cv2.waitKey(3)


    try:
      self.image_pub.publish(self.bridge.cv2_to_imgmsg(cv_image, "bgr8"))
    except CvBridgeError as e:
      print(e)

def main(args):

  ic = image_converter()
  rospy.init_node('image_converter', anonymous=True)
  try:
    rospy.spin()
  except KeyboardInterrupt:
    print("Shutting down")
  cv2.destroyAllWindows()

if __name__ == '__main__':
    main(sys.argv)