rvizlib ImageDisplay cannot find Ogre resources

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I modified the librviz tutorial to use an ImageDisplay:

  // Create image display
  image_ = dynamic_cast<rviz::ImageDisplay*>( 
      manager_->createDisplay("rviz/Image", "image", true )->getDisplay() );
  image_->setTopic("/gscam/image_raw");

But when I run the program, the Ogre subsystem fails to find any of the resources, despite the fact that the resource loading calls in rivz::RenderSystem do in fact get called:

Texture: SelectionRect0Texture: Loading 1 faces(PF_R8G8B8A8,1x1x1) with 0 generated mipmaps from Image. Internal format is PF_A8R8G8B8,1x1x1.
Texture: SelectionManagerFallbackMaterialPickTexture: Loading 1 faces(PF_R8G8B8,1x1x1) with 0 generated mipmaps from Image. Internal format is PF_X8R8G8B8,1x1x1.
terminate called after throwing an instance of 'Ogre::FileNotFoundException'
  what():  OGRE EXCEPTION(6:FileNotFoundException): Cannot locate resource no_image.png in resource group General or any other group. in ResourceGroupManager::openResource at /tmp/buildd/ros-fuerte-visualization-common-1.8.4/debian/ros-fuerte-visualization-common/opt/ros/fuerte/stacks/visualization_common/ogre/build/ogre_src_v1-7-3/OgreMain/src/OgreResourceGroupManager.cpp (line 753)

Are the resources being unloaded somewhere, or do I need to do something else to make sure they're loaded?