The Cisco Aironet 1231AG Access Point (AP) is not 802.3af compliant by default
So as a workaround, you may need to use the PowerDsine midspan.
Most Cisco Aironet APs use inline PoE from power injectors or Cisco powered EtherSwitches, but the Cisco Aironet 350, 1100, and 1200 APs do not directly support IEEE 802.3af power sources. These APs were designed before the IEEE 802.3af power standard was ratified and must use third party products such as PowerDsine to support IEEE 802.3af power sources.
PowerDsine offers midspan power products that allow customers to deploy a combination of IEEE 802.3af powered devices and non-IEEE 802.3af powered devices such as the Cisco Aironet 1120 and 1121 APs and the Cisco Aironet 350 and 1200 Series APs.