[ros-users] rosdep no valid packages listed

Hello,

I recently started working with ROS. In the beginning I had no problem
using rosdep and installing packages, but now I started getting the
following message:

kiki@kiki-laptop:~/ros$ rosdep install pr2_gazebo
Warning: could not identify ['pr2_gazebo'] as a package
Usage: rosdep [options] <command> <args>
...
rosdep: error: No Valid Packages listed

Could anybody give me a clue what I am missing here?

Thank you,
Kirila Adamova