Transparent User Authentication through AD

Have configure user authentication using LDAP and NTLM, and also configured the policies to use Authentication, with "Authenticated, no enforce" on. Symanted DCInterface is installed in AD.

However, some end-users are still getting prompt on and off. Anyone faced this problem. NTLMv1 is enable on all clients.

Anyway to configure this box to be truely transparent and is there any log files that can be give any clue to the authentication process. The GUI does not provide any logs at all.