Silly question but have you created all the other mappings for ADSgroups?
I was getting this same error on a UNS project once, but it cleared after I created the UNSAccountB, UNSGroupB *and* the UNSAccountBinUNSGroupB and UNSGroupBinUNSGroupB mappings. Presumably the same principle applies to ADS?
Thanks for the reply. Apparently I didn't define the "many-to-many" mapping for the schema types getting the error. I had to do the following for each of the schema types. In this example, the ADSGroup schema.