I noticed that in order to get a kernel log (the correct one) you need to time your command right.
So, you should have your phone plugged in while in recovery, flash the rom, reboot. and make sure you have the computer terminal ready to (in the adb directory with the command "adb shell dmesg > dmesg.txt"). Then, while its booting you'll here the plugged in/unlpugged sound a few times on your computer. When you get to the CM9 splash screen, wait for about 20-30 sec. and you'll hear the sound of it plugged in. at that moment do the command adb shell dmesg > dmesg.txt, then it should work. hope that helped.
Note: if you didn't know, if the command went through, the dmesg.txt file will be saved in this directory:
C:\Program Files (x86)\Android\android-sdk\platform-tools\dmesg.txt
(Substitute the folder names with yours, i'm on Windows 7)