[PyMOL] PyMOL doesn't start - weird problem with shaders

Dear PyMOL users,
I'm trying to use PyMOL (open source version) 1.6.0 on Mac OSX
Mavericks, installed through MacPorts. The same happens with pymol
1.7.1 as well.
Up to yesterday everything was working perfectly fine. As far as I can
remember nothing changed, but now when I run pymol I get this:

http://pastebin.com/uFyvYQCz

 Detected OpenGL version 2.0 or greater. Shaders available.
 CShaderPrg_New-Error: vertex shader compilation failed
name='default'; log follows.
infoLog=ERROR: 0:1: '' :  #version required and missing.
ERROR: 0:1: 'attribute' : syntax error syntax error

I also tried this:
And then PyMOL crashes. I have then tried the following:

- reinstalled PyMOL 1.6.0
- removed PyMOL 1.6.0 and installed 1.7.1
- updated the XQuartz X server to the latest version
- reinstalled the XQuartz X server to an older version
- wiped MacPorts and reinstalled PyMOL and its prerequisites from scratch
- installed the gfxCardStatus program and tried both using the
integrated gpu and the discrete one
- searched on the internet (of course :) )

Any idea of where this problem might come from or how I could solve it?

Thank you

Matteo