Grouping rectangle and textframe type

Below code for simple grouping objects is not working.

ID Server CS4

Vb.net

Dim FigGp As InDesignServer.Objects
Dim obj As InDesignServer.Objects
obj.Add(rect.Index) 'throwing exception Object reference not set to an instance of an object.
obj.Add(CaptionFrame)
FigGp = ParentPage.Groups.Add(obj)

Regards,

Suresh