Blair,

> The "can't find authenticator" simply means, IIRC, that the X server
> making the request is no longer running. ;)  For instance, this can

To be more specific, it means that the X servers makes a request that 
crashes and then the DRI is not happy. It seems a reasonable course.

> If you send DRI debug output from your message buffer and an Xorg log,
> we could probably help more.

I made that in a further message. There seems to be a rat race or 
something between two threads in xlock. I have rebuild xlock using the 
new mesa libs, I'll try to see if the problem remains.

Vincent