1) Is there a call $user = $userob -> authenticate(...) before the code you provided above? If so, could you show me exactly what it looks like?
2) I assume that you want the page to be accessible by both administrators and users in the 'Members' group?
3) What's the ID of the 'Members' group? You can determine that with the query: SELECT G_Name,G_Id FROM w3t_Groups WHERE G_Name='Members'