Thanks for your suggestions kdisc98!
I answer to your questions here:
1. What ARUBAOS are you using?
The controllers have the 6.1.3.5 version
2. Are u using CONTROL-PLANE SECURITY?
Yes, i'm using CONTROL-PLANE SECURITY, but i don't think this is the problem because in the past 5 months it works fine. Also, the AP MAC Address is in the whitelist campus AP.
If the problem is CONTROL-PLANE SECURITY, i think that the AP doesn't go UP for a some minutes.
Do u have LMS / BACKUP LMS Configured in your ap-default system profile?
Yes, I configure LMS / BACKUP LMS in the ap system profile. Other APs in fact works fine, so I think this is not the problem
3.Are u sure your DHCP SERVER (that is on the controller) isn't giving the same address to other unit/user on site? (might happen if broadcast is blocked in some old ArubaOS versions)
It seems that the IP isn't duplicated. But i must verify this. Broadcast isn't blocked
4.Can u check if this AP is connected via 10Mbps 100Mbps or 1000Mbps connectivity? - you might an lan infrastructure issue. -> to be sure take this AP and connect it to a different port/location - if the problem stops - so u got infrastructure problems.
I monitor from remote site the switch on wich the AP is connected; there isn't any error on port where the AP is connecteded.
This afternoon I will go to the client and so I can verify more completly if the problem is in the lan infrastructure (even if I have some doubt on this solution...)
I note that when the problematic AP goes UP in the LOCAL controller, if i execute the commmand "show ap database" in the CLI of the MASTER controller this AP isn't displayed in the list; is it normal?
In the LOCAL controller CLI, with the same command, it is displayed instead.
But if i execute "show switches", the controllers status is UPDATE SUCCESSFUL.