I spent whole weekend trying to figure out problem with my ethernet card and 2.6.12 Linux kernel.
My card worked with 2.6.11. But dmesg always showed receiver/transmission errors from the kernel. When I upgraded to 2.6.12, my card would get detected but it could not get IP address from my wireless access point.
Uh!! that was frustrating. I went to Google,kernel IRC room, kernel mailing list, Mandriva mailing list. I got no answers.
Ultimately, I decided to fix it on my own. After several hours of hacking, I found that I was loading wrong driver for my ethernet card. Davicom based ethernet card used tulip driver in kernel versions prior to 2.6.11. Certain updates in tulip drivers were not compatible with davicom chipsets. Hence I had to use native driver for davicom chipsets (which I never knew exists).
Only one word change in /etc/modprobe.conf file fixed the problem.
Now my Linux machine is back up again boasting in its usual pride.