glSetFenceNV is a nvidia graphics driver function (ask
google for further information). So I suspect that you have nvidia drivers installed alongside your ati drivers or at least some parts of the nvidia drivers are (perhaps from a former install) still present on your system. Check that there are no leftovers - especially look out for /usr/lib/libGL.so.1.2. This shared library exist in several versions - each adapted for the specific graphics board and driver. Perhaps your libGL.so is not from ATi, but from nvidia?
HTH
Greetings
Skildron