If Layar app is missing in the Android market after Android version upgrade, you should kill (remove) your market cache by running the following commend line in the terminal:

rm -r /data/data/com.android.vending/cache

For more information, please visit http://wiki.cyanogenmod.com/index.php?title=Troubleshooting.

Please note that if it is not an official upgrade, please contact your custom firmware developers to see why Layar is not shown in the Android market.