Join AD with Fortigate 40-F, DNS Problems

Hello Community,

i am absolute newbie to Fotigate. My network configuration is as follows:

The domain controller is located at the NAS1 192.168.17.201, the domain is local.XXXX.it.

My DNS settings are as follows: 

However, when I ping my domain controller with execute ping local.XXXX.it I get a response from the IP of the host of my website www.XXXX.it (courtesy page). What is wrong here?

In fact, I cannot register to the LDAP Server:

Anyone can help?

Thanks in advance.