which openGL-drivers are you using ? which openGL-headers do you use to compile Gem ? (nvidia's ???)
this is an old ati mach 64 chip on my laptop and i m using the experimental dri drivers from http://www.retinalburn.net/linux/dri_xv.html mach64-0-0-6-branch
so i guess this opengl extension is then not supportet. i ll compile it without the ogl stuff then.
best
e