Thanks a lot for posting that. We have just started trying to fix
the same problem. The fix worked for us.
For others benefit, the problem is with XFree86 4.3 and the current
NVidia driver. 4.3 comes with fedora and is in rawhide.
You get a message like:
Xlib: extension "XFree86-DRI" missing on display ":0.0"
The quick solution is to remove /usr/X11R6/lib/tls
You may need to then run ldconfig, we didn't.
glxinfo is a nice utility to let you see if DRI is enabled, of course
you could just run your visad app also.