We also use WINS. But implemented a master domain model where the user account all exist in the parent domain and computers live in country level resouce domains. We do no see the problem you describe.
When I have seen the error you listed in other application dev work, it has always been name resolution issues.
What happens if you use "domain.com\GroupName" where domain.com is the filly qualified domain name. I am not sure if KiXtart would handle this or not.
