chris@chris-desktop:~$ Xgl :2 -ac -accel xv:fbo -accel glx:pbuffer
X Error of failed request:  BadLength (poly request too large or internal Xlib length error)
  Major opcode of failed request:  148 (GLX)
  Minor opcode of failed request:  2 (X_GLXRenderLarge)
  Serial number of failed request:  89
  Current serial number in output stream:  98