ATI now belongs to AMD. Download the proprietary driver from http://ati.amd.com . Recently the (open source) radeon driver shipped with Xorg has improved DRI capabilities that are sufficient for crystallographic purposes.
using Xorg ATI driver on Mandriva 2010, coot works without the error:
'The error was 'BadRequest (invalid request code or no such operation)'.
(Details: serial 661 error_code 1 request_code 143 minor_code 19)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)'
Disable 3D desktop effects is recommanded (which did not work anyway on mandriva 2010 wit ATI card), otherwise you get a blank screen and have to undo the settings via terminal. Furthermore, do not try to use the proprietary ATI 'fglrx' drivers, since they made things even worse, at least in my personal experience (with an ATI Radeon X1650).