did you try to set the AP to factory default.
Additionally remove it from the Controller WebGui as well.
Maybe the AP tries a FW upgrade in the backgound.
So enable controlled upgrade and look if this helps.
It could be also a MTU issue?!
Try the first 2 and then we can look further.
This will point your AP's to the controller no matter what vlan/subnet they are on as long as they can resolve the name. Also, when deploying to a remote site, it is good to start your MTU Size at 1400. Anything higher than that, the AP may associate but the radios will not turn on due to packet fragmentation.
Please let us know if this does not work for you and if there is anything else we can assist you with :)
you can configure the COntoller IP staticaly on the AP.
ssh to the AP
#cset dhcpc disable
#cset ipaddr x.x.x.x ( IP for the AP itself)
#cset ipmask x.x.x.x
If the AP get his IP from a local DHCP Server you don't need do the commands above
and need only do the next command where you configure the COntroller Ip in the AP.
#set authipaddrs 1 x.x.x.x (x IP of the Controller)
Then the AP should known the COntroller IP