LDAP issue

I am trying to enable the LDAP Authentication for users to log in using AD credentials. I can establish the connection with LDAP server, and I can verify the user mapping as well. But when I use my AD username and password I get "Failed to connect to LDAP Server: No such user: A user with username ‘tuser’ does not exist". User ‘tuser’ does exist in our LDAP server.

I have LDAP Realm beneath the Local Authenticating Realm in the list.

Can someone help me what am doing wrong?

Thanks, Sushil