You have recently enabled LDAP on your Symantec Web Gateway appliance, installed the DC interface software and created policies for users, groups or organization units within your Active Directory and the policies are not being applied correctly. The authentication settings in the SWG appear to be configured correctly. The DC Interface was installed according the directions and starts with no errors.
The most likely cause for this is the computer policy for the domain controller is not configured to log the required information to the event viewer.
In the GPO for the domain controller the DC Interface software is installed on make sure the "Audit account login events" within the audit policy section is configured to log sucessful logon events.
The DC Interface software uses these events to update the Web Gateway with user information. If the events are not being logged nothing will be sent to the Web Gateway and it will not know to apply the policy.