As Allen said, LDAP is much more reliable, here is a sample of my code:
 Code:
Dim $strGroup, $objGroup, $objUser
$strGroup = "LDAP://CN=MyGroup,OU=MySecurityGroups,DC=MyDomain,DC=local"
$objGroup = GetObject($strGroup)

For Each $objUser in $objGroup.Members
  ? $objUser.CN
Next