LAP 1142N "Radio disabled due to PoE" after upgrade to 7.6.120

Question

Recently, we upgraded our 5508 wireless controllers from 7.4.110.0 to 7.6.120.0.
One AP (AIR-LAP1142N-E-K9) doesn't work now.
Both radios are stuck in state 'reset':
AP#sh int dot11Radio 0 | inc Dot11Radio0
Dot11Radio0 is reset, line protocol is down
It seems to be a PoE issue:
AP#sh controllers dot11Radio 0
Radio disabled due to PoE
This 1142N is connected to a HP switch (model 3800 with 802.3af/802.3at support). It did work on this switch several months before this upgrade and it works if connected to Cisco switch (Cat 6513).
We didn't upgrade the switch firmware or change its configuration.
The PoE status from the switch CLI:
  PoE    | Power  Power    Alloc Alloc Actual Config   Detection   Power Pre-std
  Port   | Enable Priority By    Power Power  Type     Status      Class Detect
  ------ + ------ -------- ----- ----- ------ -------- ----------- ----- ------
  21     | Yes    low      lldp  33 W  7.8 W           Delivering  3     off
Other APs (80 3602 connected to HP8212zl switches) do work without any problem.
Any idea how to solve this?

Answer 1

After updating to 7.6.120 we've noticed that some of our AP's wouldn't  come up. After looking in the switch's logs I found this
chassis: Ports  PoE usage has exceeded threshold of 80%.
The power drawn is 117w (show power-over-ethernet). 
When I use the following command: show power-over-ethernet brief I get this:
  PoE   | Power  Power    Alloc Alloc Actual Configured  Detection   Power Pre-std
  Port  | Enable Priority By    Power Power  Type        Status      Class Detect
  ----- + ------ -------- ----- ----- ------ ----------- ----------- ----- ------
  1     | Yes    low      lldp  17 W  7.0 W              Delivering  3     off
  2     | Yes    low      lldp  17 W  7.0 W              Delivering  3     off
  3     | Yes    low      lldp  17 W  6.8 W              Delivering  3     off
  4     | Yes    low      lldp  17 W  7.1 W              Delivering  3     off
  5     | Yes    low      lldp  17 W  7.0 W              Delivering  3     off
  6     | Yes    low      lldp  17 W  6.9 W              Delivering  3     off
  7     | Yes    low      lldp  17 W  6.8 W              Delivering  3     off
  8     | Yes    low      lldp  17 W  6.7 W              Delivering  3     off
  9     | Yes    low      lldp  17 W  6.9 W              Delivering  3     off
  10    | Yes    low      usage 17 W  0.0 W              Disabled    3     off
Port 10 is where the missing AP is on. 
How is it possible that after the update to 7.6.120 the AP won't work anymore?