ar_track_alvar with uvc_camera [closed]

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Hello, I want to use ar_track_alvar with uvc_camera node. Each one are working well but I cannot run both of them.

After running ar_track_alvar, uvc_camera shows error as follows:

terminate called after throwing an instance of 'std::runtime_error' what(): unable to start capture [usbcamera/uvc_camera-1] process has died [pid 9092, exit code -6, cmd /opt/ros/fuerte/stacks/camera_umd/uvc_camera/bin/camera_node __name:=uvc_camera __log:=/home/kimoon/.ros/log/02648a3a-a93d-11e2-bfc9-f04da20d7cd4/usbcamera-uvc_camera-1.log]. log file: /home/kimoon/.ros/log/02648a3a-a93d-11e2-bfc9-f04da20d7cd4/usbcamera-uvc_camera-1*.log all processes on machine have died, roslaunch will exit shutting down processing monitor... ... shutting down processing monitor complete done

FYI, I'm using a different name space for those two modules. How can I use both of them at the same time?

Thank you.