rgbdslam doesn't work if it has launched before

edit

I am following the instructions and compile all the packages successfully. Then I excute

roslaunch rgbdslam kinect+rgbdslam.launch

openni_node: /usr/include/boost/smart_ptr/shared_ptr.hpp:412: boost::shared_ptr<t>::reference boost::shared_ptr<t>::operator*() const [with T = xn::NodeInfo, boost::shared_ptr<t>::reference = xn::NodeInfo&]: Assertion `px != 0' failed.
[openni_node1-1] process has died [pid 2939, exit code -6].
log files: /home/chong/.ros/log/1ca4f8da-a515-11e1-be93-74e50b030cfa/openni_node1-1*.log

But this log file does not exit in the directory. I found another log file named roslaunch-ubuntu-3307.log and this is the part where the error possibly appears:

[roslaunch][INFO] 2012-05-23 16:28:44,034: ... successfully launched [rgbdslam-7]
[roslaunch][INFO] 2012-05-23 16:28:44,034: ... launch_nodes complete
[roslaunch.pmon][INFO] 2012-05-23 16:28:44,035: registrations completed <processmonitor(processmonitor-1, started="" daemon="" 139844188399360)="">
[roslaunch.parent][INFO] 2012-05-23 16:28:44,035: ... roslaunch parent running, waiting for process exit
[roslaunch][INFO] 2012-05-23 16:28:44,035: spin
[roslaunch][ERROR] 2012-05-23 16:28:52,215: [openni_node1-2] process has died [pid 3346, exit code -6].
log files: /home/chong/.ros/log/e41573d6-a515-11e1-8e5f-74e50b030cfa/openni_node1-2*.log
[roslaunch.pmon][INFO] 2012-05-23 16:28:52,216: ProcessMonitor.unregister[openni_node1-2] starting
[roslaunch.pmon][INFO] 2012-05-23 16:28:52,216: ProcessMonitor.unregister[openni_node1-2] complete

The interesting thing is, when I restart the system and try this again, it works the first time, but if I try roslaunch the second time, tthen the same error appears. Seems it only works at the first time after the system is booted. I guess I didn't shut down everything executed by the first time roslaunch but I don't know how to do it. Anybody knows how to solve this? I will appreciate any suggestions !

Edit: after I type ^C in the window, it says

[rgbdslam-7] killing on exit
[kinect_base_link3-6] killing on exit
[kinect_base_link2-5] killing on exit
[kinect_base_link1-4] killing on exit
[kinect_base_link-3] killing on exit
[rosout-1] killing on exit
[master] killing on exit
shutting down processing monitor...
... shutting down processing monitor complete
done