The reason you are receiving this error, you are running PowerShell command from Child domain and you like to see the Groups located on the root domain. In order to see these groups and continue to carry on your task all you need to do it to change your setting to view entire forest, this is almost same as opening ADUC and trying to located users or groups within the child domain, when these users or groups actually sits on the root domain. You don’t see it because your query is being performed on the child domain only.
see the settings
|Get-AdServerSettings | fl|
To change that
|Set-AdServerSettings -ViewEntireForest $True|
Now you wont have the errors if you carry on the same task
Oz Casey, Dedeal
( Exchange Server North America MVP)