If you use the CE500's PoE alone (without the power injector) does the port comes up or the AP powers up? Without additional info, I can only offer the following:
Intelligent Power Management support is dependent on the version of software resident in the Cisco switch that is providing power to the access point. Each Cisco switch should be upgraded to support Intelligent Power Management. Until the software is upgraded, you can use your controller to configure the access point to operate with older switch software using these controller CLI commands:
1) config ap power pre-standard enable
where is the access point name on the controller
2) config ap power injector enable
(where is the access point name on the controller
and is the MAC address of the switch port to which the
access point is connected)
http://www.cisco.com/en/US/docs/wireless/access_point/1250/installation/guide/125h_c4.html