The %ILPOWER-3-CONTROLLER_ERR: Controller error, Controller number [chars]: accessing failed error message means that an error reported or caused by the inline power controller was detected.
When a Cisco Catalyst 3550-24 PWR interface receives an Electrostatic Discharge (ESD) from a device (such as a powered IP phone), some interfaces go down no longer provide power.
This is a software defect and is documented in Cisco bug ID CSCea40671.
To resolve the issue, consider these options:
Syslog error message received