Select the RID option when joining the ADS with DSS V7.
RID (relative identifier) - generates unique UIDs and GIDs based on the Relative Identifier (RID) part of a Windows SID. Provides the same mapping of UIDs and GIDs on different hosts.
See is the steps in this KB will help, if not we may need to see the log file of the DSS (log a ticket in your User Portal) to see why you are not able to connect to the ADS, also try with PDC just to see if you can connect to the ADS.