What software version is this IAP? You could be running an older version of IAP where the channel selection is not so good.
What is your regulatory domain? That will determine how many 80Mhz channels you have.
You are running 80mhz channels (E) in the 5ghz, so your channel choices are limited because you are bonding channels. You should go to RF> ARM and change "80Mhz Support" to "Disabled". You would then have 40Mhz channels on 802.11a (+/-) and give access points 20 minutes try to change to another channel.
Go to More> Support, then run "AP ARM RF Summary" command on each access point. Under Channel Summary, there is an intf_indx column. The last number in parentheses () says how much interference each access point sees on a channel. It is possible that your access points see too much interference on channel 11 to put an access point on that channel.
A short document on how ARM works is here: http://community.arubanetworks.com/aruba/attachments/aruba/70/1204/1/ARM+Doc+Supplement.pdf