2 webcam feed doesn't work opencv

I'm using ubuntu 13.10 along with opencv 2.4.9 with python 2.7.I have written the following code but it seems to fails on runtime.

  import cv2  c1=cv2.VideoCapture(2) #camera id  c2=cv2.VideoCapture(1) #camera id  while(True):      ret,frame = c1.read()      ret,frame2 = c2.read()      frame = cv2.cvtColor(frame,0)      frame2 = cv2.cvtColor(frame2,0)      cv2.imshow('frame',frame)      cv2.imshow('frame2',frame2)      if cv2.waitKey(1) & 0xFF == ord('q'):            break  c1.release()  c2.release()  cv2.destroyAllWindows()

But on running this in Ubuntu i get the following error :

  VIDIOC_QUERYMENU: Invalid argument  libv4l2: error turning on stream: Invalid argument  VIDIOC_STREAMON: Invalid argument  OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, file     /build/buildd/opencv-2.4.5+dfsg/modules/imgproc/src/color.cpp, line 3358  Traceback (most recent call last):  File "/home/bini/KV/IP_Proj/webcam basics opencv.py", line 8, in <module>  frame2 = cv2.cvtColor(frame2,0)   cv2.error: /build/buildd/opencv-2.4.5+dfsg/modules/imgproc/src/color.cpp:3358: error:        (-215) scn == 3 || scn == 4 in function cvtColor

The same code used to work fine on windows.Can someone help me please as to why is this occuring..??? i have on idea.

Thanks in advance