Call was rejected by Callee - Delphi, Excel

The Problem that i am facing that within my delphi application i am
calling excel inside my OLE Container. And then on the top of that i
want to plot charts but the actual problem comes at the time i run the
EXE.If i put brakepoints then it runs but after that it stops
running.It give the error "Call rejected By Calle" and also that "The
Operation is completed successfully."Why is that happening.

App := FOleContainer.OleObject.Application;
  objExcel := FOleContainer.OleObject ;
  ActiveWnd := App.ActiveWindow;
  mychart := objExcel.Charts.Add ;
  mychart.ChartType := -4169;
  mychart.SeriesCollection(1).Trendlines.Add(-4132);
  mychart.HasTitle:= True;
  mychart.Charttitle.Characters.Text:='Scatter Diagram';

If i remove the "  mychart.HasTitle:= True; &  
mychart.Charttitle.Characters.Text:='Scatter Diagram';
" option then it runs successfully.

Please let me knw ASAP.ITS URGENT