How to run explore_stage demo so that PR2 can navigate in the environment automatically

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I followed this page to run the demo of explore_stage on Ubuntu 12.04 with ros fuerte installed. (I want to let PR2 navigate in the environment automatically)

I tried two commands below

roslaunch explore_stage explore.launch

roslaunch explore_stage explore_slam.launch

but I bumped into similar errors indicating that laser model not found in both cases and the stage simulator would die. The error messages look like:

err: Model type laser not found in model typetable (/tmp/buildd/ros-fuerte-stage-1.6.6/debian/ros-fuerte-stage/opt/ros/fuerte/stacks/stage/build/stage/libstage/world.cc CreateModel)
err: Unknown model type laser in world file. (/tmp/buildd/ros-fuerte-stage-1.6.6/debian/ros-fuerte-stage/opt/ros/fuerte/stacks/stage/build/stage/libstage/world.cc CreateModel)
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[move_base-4]: started with pid [10744]
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[explore-5]: started with pid [10762]
[ INFO] [1366388374.725280598]: Subscribed to Topics: base_scan
[stage-2] process has died [pid 10664, exit code 1, cmd /opt/ros/fuerte/stacks/stage/bin/stageros /opt/ros/fuerte/stacks/bosch_common/bosch_worlds/maze-noisy.world __name:=stage __log:=/home/rosfuerte/.ros/log/eaa67974-a90c-11e2-a83d-c860003a5122/stage-2.log].
log file: /home/rosfuerte/.ros/log/eaa67974-a90c-11e2-a83d-c860003a5122/stage-2*.log

The detail output messages are:

explore.launch detail messages

explore_slam.launch detail messages

How to solve this problem? Thanks.