Issue with usb_cam, can't open camera

edit

I wanna to test whether this usb_cam works. But get the error below. Anyone can help? THX!!

@Laptop:~/ros_workspace/usb_cam$ roslaunch usb_cam-test.launch
... logging to /home/lanray/.ros/log/cb16e5d0-f5e3-11e1-bc19-001e64868dfe/roslaunch-Laptop-18031.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server <a href="http://Laptop:56876/">http://Laptop:56876/</a>

SUMMARY
========

PARAMETERS
 * /image_view/autosize
 * /rosdistro
 * /rosversion
 * /usb_cam/camera_frame_id
 * /usb_cam/image_height
 * /usb_cam/image_width
 * /usb_cam/io_method
 * /usb_cam/pixel_format
 * /usb_cam/video_device

NODES
  /
    image_view (image_view/image_view)
    usb_cam (usb_cam/usb_cam_node)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[usb_cam-1]: started with pid [18051]
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[image_view-2]: started with pid [18062]
usb_cam video_device set to [/dev/video0]
usb_cam io_method set to [mmap]
usb_cam image_width set to [640]
usb_cam image_height set to [480]
usb_cam pixel_format set to [mjpeg]
usb_cam auto_focus set to [0]
VIDIOC_S_FMT error 22, Invalid argument
[usb_cam-1] process has died [pid 18051, exit code 1, cmd /home/lanray/ros_workspace/usb_cam/bin/usb_cam_node __name:=usb_cam __log:=/home/lanray/.ros/log/cb16e5d0-f5e3-11e1-bc19-001e64868dfe/usb_cam-1.log].
log file: /home/lanray/.ros/log/cb16e5d0-f5e3-11e1-bc19-001e64868dfe/usb_cam-1*.log