When you start YASARA under Linux and get the message

Xlib: extension "XFree86-DRI" missing on display ":0.0"

this indicates that your OpenGL driver is not installed properly. This happens for example when installing an old nVIDIA driver on a new Linux distribution with Kernel 2.6, e.g. Fedora Core 1. Do not ignore the message, you may encounter serious graphics problems and system hangs. Instead update to the latest driver.

If you absolutely have to use an old driver (for example because of stereo support), you can still modify the old nVIDIA driver to work with a new kernel: http://www.minion.de/nvidia.html and http://sh.nu/download/nvidia/linux-2.6/