Answered my own question.
The SD-Card Linux Image to Enable WiFi is missing iwlwifi-6000g2b-6.ucode
It only has iwlwifi-6000g2a-6.ucode.
Added iwlwifi-6000g2b-6.ucode. to /lib/firmware on board and it now works.
if I reboot the board, the file iwlwifi-6000g2b-6.ucode in /lib/firmware is missing.
the message "WIFI shield not present" are still printed out.
I copied the file into the directory.