Unable to find shader lib. Error in Gazebo

I am facing below error when I try to run gazebo any help regarding this is highly appreciated Error [RTShaderSystem.cc:408] Unable to find shader lib. Shader generating will fail.terminate called after throwing an instance of 'Ogre::ItemIdentityException' what(): OGRE EXCEPTION(5:ItemIdentityException): Cannot locate material called 'Gazebo/shadow_caster' in SceneManager::setShadowTextureCasterMaterial at /build/buildd/ogre-1.7.4/OgreMain/src/OgreSceneManager.cpp (line 5833)