ios - Shared iAd Banner doesn't appear between TableViews -

based on tutorial @ http://www.youtube.com/watch?v=u5xcvnhcq0w , implemented shared iad banner view show between header position of 2 tables. 2 table controllers under navigation controller. banner view showing in first table, not showing in next table.

same code implemented in uitableviewcontrollers

     - (appdelegate *) appdelegate {         return (appdelegate *)[[uiapplication sharedapplication] delegate];     }       -(cgfloat)tableview:(uitableview *)tableview heightforheaderinsection:(nsinteger)section{       return 100.0;     }      -(void) viewwillappear:(bool)animated{         _uiiad = [[self appdelegate] uiiad];         _uiiad.delegate = self;          [_uiiad setframe:cgrectmake(0,21,320,50)];         [self.view addsubview:_uiiad];     }      -(void) viewwilldisappear:(bool)animated{         _uiiad.delegate = nil;         _uiiad=nil;         [_uiiad removefromsuperview];     }      -(void)bannerviewdidloadad:(adbannerview *)banner{         nslog(@"ads loaded");         [uiview beginanimations:nil context:nil];         [uiview setanimationduration:1];         [_uiiad setalpha:1];         [uiview commitanimations];     }      -(void)bannerview:(adbannerview *)banner didfailtoreceiveadwitherror:(nserror *)error{         nslog(@"ads not loaded");         [uiview beginanimations:nil context:nil];         [uiview setanimationduration:1];         [_uiiad setalpha:0];         [uiview commitanimations];     }