When upgrading to 2.6.25-git18 and above kernel this Xorg error occurs :

xf86MapVidMem: Could not mmap framebuffer (0xf0000000,0x8000000) 
(Invalid argument)

The latest working kernel was 25-git17 and perhaps is it related to 
http://lkml.org/lkml/2008/4/28/52

My .config and Xorg-log files are attached.

Best regards.