Not knowing what you have tried, have you considered the following?
Is this a new problem on an old install? If so, have you experienced power losses/surges? Is logging enabled on the AP and device (switch/hub) connected to the AP FastE interface? Do the AP and switch logs provide any clues? Did you recently upgrade the hardware/software of the connected switch? Are there any devices or patch panels between the AP and switch? Are there a lot of CRC/input/output errors on the AP and/or switch interfaces. Did the Ethernet cable get damaged? Are the AP and switch interfaces configured to auto-negotiate speed/duplex? Are you using power-over-ethernet for the AP? Have you tried another switch-port on another ASIC? Is the AP being authenticated via 802.1x with re-authentication at 8-9 minute intervals? Is the AP overheating, is there sufficient ventilation?
hth
