Sharepoint 2007 Custom permission level to manage permissions

I have a problem: I need to add custom permission level to sharepoint, that grants access to manage permissions and view (read only) pages.

The permission levels that I set to the permission level are:

                    SPBasePermissions.Open
                                | SPBasePermission开发者_如何学编程s.ApproveItems
                                | SPBasePermissions.ViewListItems
                                | SPBasePermissions.OpenItems
                                | SPBasePermissions.ViewVersions
                                | SPBasePermissions.ViewPages
                                | SPBasePermissions.BrowseDirectories
                                | SPBasePermissions.EnumeratePermissions
                                | SPBasePermissions.BrowseUserInfo
                                | SPBasePermissions.CreateGroups
                                | SPBasePermissions.ViewFormPages
                                | SPBasePermissions.ManagePermissions;

I can Add Groups but "Add user" is unvisible. What I am missing here?

thx!

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also include SPBasePermissions.ManageLists