You may be running into one of these reasons why the 1231 isn't supporting WPA2;
Q. What Cisco Aironet access points support WPA2 and AES?
A. The following Cisco Aironet autonomous and lightweight access points support WPA2 and AES: Cisco Aironet 1240AG Series, 1230AG Series, 1130AG Series and 1000 Series access points. Cisco Aironet 1100 Series, 1200 Series and 1300 Series 802.11g radios support WPA2 with a Cisco IOS Software upgrade via Cisco IOS Software Release 12.3(2)JA or later.
Q. Which Cisco Aironet 1200 Series 802.11a radio modules support WPA2 and AES?
A. Cisco Aironet 1200 Series radio modules with the part numbers AIR-RM21A or AIR-RM22A support WPA2 and AES. The Cisco Aironet 1200 Series radio module with the part number AIR-RM20A does not support WPA2 or AES.
Q. Which Cisco Aironet 802.11b access points support WPA2 and AES?
A. Cisco Aironet 802.11b access points are not upgradeable to support WPA2 and AES.