sdf model is not showing up correct

Hi, I am not able to inserting my sdf model correctly into Gazebo7. If I start my model as a world file including the ground_plane and the sun it is showing up properly. model://ground_planemodel://sun .......  As soon I am trying to start it as a model it will be displayed as boxes. Only changes is the following code: ......  The MODEL_PATH is set correctly, it also displays the correct name of the model-file which typed into the .config file. Maybe somebody can help me???