I am experiencing this annoying behaviour from the ati proprietary driver (fglrx) on my laptop (HP NX9420 with the Radeon Mobility X1600 graphics chip). Firstly, I was only able to get 3D acceleration as root user even with the code below in the xorg.conf file.

Section "DRI"
Mode 0666
EndSection

When I run glxgears as root everything worked fine. However as a regular user, although the frame-rate was similar to that which was obtained as root, I also got a long list of the following errors:

FGLTexMgr: open of shared memory object failed (Permission denied)
__FGLTexMgrCreateObject: __FGLTexMgrSHMmalloc failed!!!

Anyway I did a bit of searching and I was able to solve that problem by adding:

tmpfs /dev/shm tmpfs defaults 0 0

to the /etc/fstab file. Now 3D acceleration works for all users.

However, I am still having this annoying problem whereby when I switch between desktop environments e.g. KDE and XFCE (or GNOME from this forum), hardware acceleration stops working (even for root) and the desktop environment crashes and is dumped to the an unresponsive console. As an example, if tuxracer is run after switching to a different desktop environment, play is quite jerky and when it is closed an unresponsive console results. Logging in via a CTRL_ALT_F6 afterwards works though with full 3D acceleration again.

I am using the latest ATI proprietary driver and have also tried the previous 2 with similar results. Any ideas anyone?

Cheers