cisco 2504 WILAN ERROR MESSAGE

[2D-Technology Services]

Dear All.,

My Cisco WLAN CONTROLLER 2504 suddenly started to De-associate Access Points. Attached herewith is the Error Message gotten from the GUI 

Let me know if anyone has solution to address this thanks.

[Mark Elsen]

 - Are you using ipv6 if not from CLI use : 

      config ipv6 disable

M.

[Leo Laohoo]

VLAN 20 DHCP scope is disabled.