If you have a firewall between your VMware Horizon 8 environment and your Active Directory server, you must make sure that all of the necessary ports are opened.
For example, the connection broker must be able to access the Active Directory Global Catalog and Lightweight Directory Access Protocol (LDAP) servers. If the Global Catalog and LDAP ports are blocked by your firewall software, administrators will have problems configuring user entitlements.
See the Microsoft documentation for your Active Directory server version for information about the ports that must be opened for Active Directory to function correctly through a firewall.