Here are my working settings. I didn't see where you said what ldap server specifics you had (AD, etc).
Default Domain: corp.DOMAIN.local
DNS Servers: ip of my dns server
LDAP Servers: ip address of my primary dc
Use TLS: checked
Search User: DOMAIN\username.
Password: my password
Search Base: OU=All_Users,DC=corp,DC=DOMAIN,DC=local
LDAP Schema: Microsoft Active Directory
My only other suggestion is that you make sure that the user that you are using has privileges to bind to the server.