Hi,
I Think you require to check the below three things
1) You have properly configured DNS IP and Domain Name in DNS and Routing Configuration
2) You have to check wether all the required ports are open for communication between the ESX/ESXi host and Active Directory:
Port 88 - Kerberos authentication
Port 123 – NTP
Port 135 - RPC
Port 137 - NetBIOS Name Service
Port 139 - NetBIOS Session Service (SMB)
Port 389 - LDAP
Port 445 - Microsoft-DS Active Directory, Windows shares (SMB over TCP)
Port 464 - Kerberos - change/password changes
Port 3268- Global Catalog search
3) Check wether you are entering the credentials properly , If you have entered the user credentials in the <domain\username> format.
To resolve this issue, enter the user credentials in the <username> or <username@fqdn_of_the_domain> format.