Activities can't be added until the containing group has been created

Activities can't be added until the containing group has been created, error

Can any one help, below is the code im using.

try{
                                Intent previewMessage = new Intent(Home.this, a.class);
                                System.out.println("preview message "+previewMessage);

                                a insA = new a();

                                TabGroupActivity parentActivity = (TabGroupActivity)insA;
                                System.out.println("parentActivity message "+parentActivity);

                                parentActivity.startChildActivity("home", previewMessage);
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                                }catch(Exception ex){
                                    System.out.println("Caought exception :- "+ex.getMessage());
                                }