OpenGL error

[cfcv]

Hi,

I'm having some trouble instantiating a gym-duckietown env on a server. I'm executing the following command:
xvfb-run -s "-screen 0 1400x900x24 +iglx" python train.py

The train.py script just creates a DuckietownLF env object for now, and I'm getting the following error:

self.multi_fbo, self.final_fbo = create_frame_buffers(self.camera_width, self.camera_height, 4)
  File "....../gym-duckietown/src/gym_duckietown/graphics.py", line 227, in create_frame_buffers
    assert res == gl.GL_FRAMEBUFFER_COMPLETE
AssertionError

if I run: xvfb-run -s "-screen 0 1400x900x24 +iglx" glxinfo | grep "version"
I got:

server glx version string: 1.4
client glx version string: 1.4
GLX version: 1.4
OpenGL version string:

So the glx version is 1.4 but the OpenGL version is strangely empty.
My mesa-utils version is 8.3.0-1.

Am I missing some flag in the xvfb-run command?

Thanks for the help!