title: OpenCV Error: Unspecified error (The node does not represent a user object (unknown type?)) in cvRead
body: <p>I have trained haarclassifier and tried to find the width and height of the pattern which I am searching for, with the following code. </p>
  
  <pre><code>import numpy as np
  import cv2
  
  
  pattern_cascade = cv2.CascadeClassifier('stage15.xml')
  
  
  img = cv2.imread('image.png')
  gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
  
  pattern = pattern_cascade.detectMultiScale(gray,1.3,5)
  (x,y,w,h) = pattern
  cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
  
  cv2.imshow('img',img)
  cv2.waitKey(0)
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>But I am getting the following error. Can somebody help me in fixing this ? </p>
  
  <pre><code>kathir@kathir-VirtualBox:~/Desktop/Haarcascade /neg and bg$ python FindPattern.py 
  OpenCV Error: Unspecified error (The node does not represent a user object (unknown type?)) in cvRead, file /build/buildd/opencv-2.4.8+dfsg1/modules/core/src/persistence.cpp, line 4991
  Traceback (most recent call last):
    File "FindPattern.py", line 5, in &lt;module&gt;
      pattern_cascade = cv2.CascadeClassifier('stage15.xml')
  cv2.error: /build/buildd/opencv-2.4.8+dfsg1/modules/core/src/persistence.cpp:4991: error: (-2) The node does not represent a user object (unknown type?) in function cvRead
  </code></pre>
  
  <p>If someone help to understand the error also, it is appreciated.</p>