osgEarth problem

#include <osgEarth/MapNode>
#include <osgEarth/FindNode>
#include <osgEarth/TileSource>
#include <osgEarth/Registry>
#include <osgEarthUtil/EarthManipulator>

#include <osgViewer/Viewer>
#include <osgViewer/ViewerEventHandlers>

#include <osgGA/StateSetManipulator>

#include <iostream>

#define SHOW_PROBLEM 1

using namespace osg;
using namespace osgEarth;
using namespace osgEarthUtil;

struct BlankTileSource : public osgEarth::TileSource
{
   BlankTileSource(const PluginOptions* options =0L) : osgEarth::TileSource( options ) { }

   virtual void initialize( const std::string& referenceURI, const Profile* overrideProfile =0)
   {
      if (overrideProfile)
      {
         setProfile( overrideProfile );
      }
      else
      {
         setProfile( osgEarth::Registry::instance()->getGlobalGeodeticProfile() );
      }
   }


   virtual osg::Image* createImage( const TileKey* key, ProgressCallback* progress ) {
      osg::Image* image = new osg::Image();
      image->setAllocationMode( osg::Image::USE_NEW_DELETE );
      image->allocateImage( 256, 256, 1, GL_RGBA, GL_UNSIGNED_BYTE );
      for( int y=0; y<image->t(); y++ ) {
         for( int x=0; x<image->s(); x++ ) {
            *((unsigned int*)(image->data(x,y))) = 0xff00ff00;
         }
      }
      return image;
   }
};

int main(int argc, char** argv)
{
   // construct the viewer.
   osgViewer::Viewer viewer();

   // construct the main scene group.
   osg::Group* group = new osg::Group;

   // construct the map.
   Map *map = new Map;

   TileSource *tileSource = new BlankTileSource();
   tileSource->initialize("");
   MapLayer* layer = new MapLayer( "Green", MapLayer::TYPE_IMAGE, tileSource);
   map->addMapLayer(layer);

   MapNode* mapNode = new MapNode(map);

   // construct pre-render texture.
   osg::Texture2D *renderTex = new osg::Texture2D;
   renderTex->setTextureSize(1024, 1024);
   renderTex->setDataVariance(osg::Object::DYNAMIC);
   renderTex->setInternalFormat(GL_RGBA);
   renderTex->setFilter(osg::Texture2D::MIN_FILTER, osg::Texture2D::LINEAR);
   renderTex->setFilter(osg::Texture2D::MAG_FILTER, osg::Texture2D::LINEAR);

   // construct pre-render camera.
   osg::Camera* camera = new osg::Camera;
   camera->setRenderOrder(osg::Camera::PRE_RENDER);
   camera->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);
   camera->setComputeNearFarMode(osg::CullSettings::COMPUTE_NEAR_FAR_USING_PRIMITIVES);
   camera->setNearFarRatio(0.000003f);
   camera->setClearColor(osg::Vec4(0.8f, 0.8f, 0.8f, 1.f));
   camera->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   camera->setViewport(0, 0, 1024, 1024);
   camera->attach(osg::Camera::COLOR_BUFFER, renderTex);
   renderTex->setDataVariance(osg::Object::DYNAMIC);
   camera->addChild(mapNode);

#if SHOW_PROBLEM == 0
   group->addChild(camera);
#endif

   // create scene.
   group->addChild(mapNode);

   // setup viewer.
   viewer.setCameraManipulator( new osgEarthUtil::EarthManipulator() );
   viewer.setUpViewInWindow(10, 10, 800, 800);
   viewer.addEventHandler( new osgViewer::StatsHandler() );
   viewer.addEventHandler( new osgViewer::WindowSizeHandler() );
   viewer.addEventHandler( new osgViewer::ThreadingHandler() );
   viewer.addEventHandler( new osgGA::StateSetManipulator(viewer.getCamera()->getOrCreateStateSet()) );

   // set the scene to render.
   viewer.setSceneData(group);

   // run the viewers frame loop.
   return viewer.run();
}