I had just installed ros-fuerte-desktop-full, which comes with Gazebo, and being fairly new to ROS and Gazebo, was testing/playing around with Gazebo via the command

$ roslaunch gazeboworlds emptyworld.launch

It worked for a bit, then when I went to add actor.model, it crashed and I killed the process. I tried to open it again with the same command, but now I can no longer get it to work correctly. When it opens, the visualization screen is often black, and even when the visualization screen displays the empty world appropriately (which has only happened once), the addition of some models either return errors or cause it to crash entirely.

Here's an example of the results I get when I try to run it with the command above. When I added the Pioneer, it produced the "Error [ColladaLoader.cc:1392] No Opaque Set" error, and then the addition of actor.model caused it to crash. I killed it at the end:

$ roslaunch gazebo_worlds empty_world.launch
... logging to /home/hdaepp/.ros/log/112964a2-1efd-11e2-acbc-000c297df36a/roslaunch-ubuntu-3960.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://ubuntu:57194/

SUMMARY
========

PARAMETERS
 * /rosdistro
 * /rosversion
 * /use_sim_time

NODES
  /
    gazebo (gazebo/gazebo)
    gazebo_gui (gazebo/gui)

auto-starting new master
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[master]: started with pid [3976]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to 112964a2-1efd-11e2-acbc-000c297df36a
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[rosout-1]: started with pid [3989]
started core service [/rosout]
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[gazebo-2]: started with pid [4003]
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
process[gazebo_gui-3]: started with pid [4009]
Gazebo multi-robot simulator, version 1.0.2
Copyright (C) 2011 Nate Koenig, John Hsu, Andrew Howard, and contributors.
Released under the Apache 2 License.
http://gazebosim.org

Gazebo multi-robot simulator, version 1.0.2
Copyright (C) 2011 Nate Koenig, John Hsu, Andrew Howard, and contributors.
Released under the Apache 2 License.
http://gazebosim.org

Msg Waiting for master.Msg Waiting for master[ INFO] [1351208305.277895326]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...

Msg Connected to gazebo master @ http://localhost:11345
[ INFO] [1351208305.494325660]: joint trajectory plugin missing <updateRate>, defaults to 0.0 (as fast as possible)

Msg Connected to gazebo master @ http://localhost:11345
[ INFO] [1351208307.029034717, 0.031000000]: waitForService: Service [/gazebo/set_physics_properties] is now available.
[ INFO] [1351208307.164583107, 0.726000000]: Starting to spin physics dynamic reconfigure node...
LightListWidget::OnLightMsg
Error [ColladaLoader.cc:1392] No Opaque set
Error [ColladaLoader.cc:1392] No Opaque set
Error [ColladaLoader.cc:1392] No Opaque set
Error [ColladaLoader.cc:1392] No Opaque set
/opt/ros/fuerte/stacks/simulator_gazebo/gazebo/scripts/gui: line 2:  4013 Segmentation fault      (core dumped) `rospack find gazebo`/gazebo/bin/gzclient -g `rospack find gazebo`/lib/libgazebo_ros_paths_plugin.so
[gazebo_gui-3] process has died [pid 4009, exit code 139, cmd /opt/ros/fuerte/stacks/simulator_gazebo/gazebo/scripts/gui __name:=gazebo_gui __log:=/home/hdaepp/.ros/log/112964a2-1efd-11e2-acbc-000c297df36a/gazebo_gui-3.log].
log file: /home/hdaepp/.ros/log/112964a2-1efd-11e2-acbc-000c297df36a/gazebo_gui-3*.log