Hi everyone,<br /><br />My name is Grace Lee and I am an undergraduate research assistant at USC&#39;s Interaction Lab. I am currently writing a urdf for a human model that will be interacting with PR2 in the gazebo. When I run the command &quot;roslaunch&quot; on my launch file, I get this error: [ERROR] 1277225053.038870000: Could not compute link poses. The tree or the state is invalid.<br /><br />I have parsed the urdf and the tree structure seems correct - i.e.   $ rosrun urdf check_urdf [my_urdf_name].xml   shows that there is one child (which is correct btw). The urdf and the state_publisher.cpp seems to be correct as well. Any insights into the source of this problem would be greatly appreciated.<br /><br />Sincerely,<br /><br />Grace Lee