error:can't load nodelet openni_launch "navigation" [closed]

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hello,

I'm trying to do tutorial : SLAM Map Building with Turtlebot.

i'm using ubuntu11.10 and ROS fuerte

when i do this command

roslaunch turtlebot_navigation gmapping_demo.launch

i have this error

error:can't load nodelet/openni_launch for one exists with that name already

and when i opened rviz ,camera worked normally but no maps appear although i teleop the turtlebot

i need help,

thanks in advance