Ok, found the issue! actually I changed hostname (Zentyal) to DNW after provision the domain name and openchange. After checking the LDAP setting, the Root DN still pointing to cn=zentyal, by adding the previous hostname (zentyal) into the DNS module the message disappeared and new config page shown allow u to set "Access with/without SSL"
Great! now l can try my outlook anywhere. some people say this is useless function, but it still benefit to those carrying laptop to check their email. also looking forward for Zentyal 3.5 for active sync, which already have in SOGo 2.2.
I think this also disclose the issue that changing the hostname in zentyal will not apply the setting to ldap or openchange ??
Anyway, will mark this post as SOLVED if no any other issue related to RPC proxy.