title: OpenGL glValidateProgram error on Mac OS X
body: <p>I am trying to write a simple OpenGL 3.2 (with GLSL 1.5) program using GLUT on Mac OS X (Mountian Lion), but I keep getting error from glValidateProgram:</p>
  
  <p>'Validation Failed: Current draw framebuffer is invalid.'</p>
  
  <p>What could cause this error to occur?</p>